User manual | SCXI-1200 User Manual - Artisan Technology Group

SCXI™-1200
User Manual
12-Bit Data Acquisition and Control Module
SCXI-1200 User Manual
December 1996 Edition
Part Number 320673C-01
© Copyright 1993, 1996 National Instruments Corporation. All Rights Reserved.
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Important Information
Warranty
The SCXI-1200 is warranted against defects in materials and workmanship for a period of one year from the date of
shipment, as evidenced by receipts or other documentation. National Instruments will, at its option, repair or replace
equipment that proves to be defective during the warranty period. This warranty includes parts and labor.
The media on which you receive National Instruments software are warranted not to fail to execute programming
instructions, due to defects in materials and workmanship, for a period of 90 days from date of shipment, as evidenced
by receipts or other documentation. National Instruments will, at its option, repair or replace software media that do
not execute programming instructions if National Instruments receives notice of such defects during the warranty
period. National Instruments does not warrant that the operation of the software shall be uninterrupted or error free.
A Return Material Authorization (RMA) number must be obtained from the factory and clearly marked on the outside
of the package before any equipment will be accepted for warranty work. National Instruments will pay the shipping
costs of returning to the owner parts which are covered by warranty.
National Instruments believes that the information in this manual is accurate. The document has been carefully
reviewed for technical accuracy. In the event that technical or typographical errors exist, National Instruments reserves
the right to make changes to subsequent editions of this document without prior notice to holders of this edition. The
reader should consult National Instruments if errors are suspected. In no event shall National Instruments be liable for
any damages arising out of or related to this document or the information contained in it.
EXCEPT AS SPECIFIED HEREIN, NATIONAL INSTRUMENTS MAKES NO WARRANTIES, EXPRESS OR IMPLIED, AND
SPECIFICALLY DISCLAIMS ANY WARRANTY OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
CUSTOMER’S RIGHT TO RECOVER DAMAGES CAUSED BY FAULT OR NEGLIGENCE ON THE PART OF NATIONAL
INSTRUMENTS SHALL BE LIMITED TO THE AMOUNT THERETOFORE PAID BY THE CUSTOMER. NATIONAL INSTRUMENTS
WILL NOT BE LIABLE FOR DAMAGES RESULTING FROM LOSS OF DATA, PROFITS , USE OF PRODUCTS, OR INCIDENTAL OR
CONSEQUENTIAL DAMAGES , EVEN IF ADVISED OF THE POSSIBILITY THEREOF. This limitation of the liability of National
Instruments will apply regardless of the form of action, whether in contract or tort, including negligence. Any action
against National Instruments must be brought within one year after the cause of action accrues. National Instruments
shall not be liable for any delay in performance due to causes beyond its reasonable control. The warranty provided
herein does not cover damages, defects, malfunctions, or service failures caused by owner’s failure to follow the
National Instruments installation, operation, or maintenance instructions; owner’s modification of the product;
owner’s abuse, misuse, or negligent acts; and power failure or surges, fire, flood, accident, actions of third parties, or
other events outside reasonable control.
Copyright
Under the copyright laws, this publication may not be reproduced or transmitted in any form, electronic or mechanical,
including photocopying, recording, storing in an information retrieval system, or translating, in whole or in part,
without the prior written consent of National Instruments Corporation.
Trademarks
LabVIEW®, NI-DAQ®, RTSI®, CVI™, and SCXI™ are trademarks of National Instruments Corporation.
Product and company names listed are trademarks or trade names of their respective companies.
WARNING REGARDING MEDICAL AND CLINICAL USE OF NATIONAL INSTRUMENTS PRODUCTS
National Instruments products are not designed with components and testing intended to ensure a level of reliability
suitable for use in treatment and diagnosis of humans. Applications of National Instruments products involving
medical or clinical treatment can create a potential for accidental injury caused by product failure, or by errors on the
part of the user or application designer. Any use or application of National Instruments products for or involving
medical or clinical treatment must be performed by properly trained and qualified medical personnel, and all traditional
medical safeguards, equipment, and procedures that are appropriate in the particular situation to prevent serious injury
or death should always continue to be used when National Instruments products are being used. National Instruments
products are NOT intended to be a substitute for any form of established process, procedure, or equipment used to
monitor or safeguard human health and safety in medical or clinical treatment.
Table
of
Contents
About This Manual
Organization of This Manual ........................................................................................ ix
Conventions Used in This Manual................................................................................ x
National Instruments Documentation ........................................................................... xi
Related Documentation................................................................................................. xii
Customer Communication ............................................................................................ xii
Chapter 1
Introduction
About the SCXI-1200 ................................................................................................... 1-1
What You Need to Get Started ..................................................................................... 1-2
Software Programming Choices ................................................................................... 1-2
LabVIEW and LabWindows/CVI Application Software............................... 1-3
NI-DAQ Driver Software ............................................................................... 1-3
Register-Level Programming ......................................................................... 1-4
Optional Equipment ...................................................................................................... 1-5
Custom Cables................................................................................................ 1-5
Unpacking ..................................................................................................................... 1-6
Chapter 2
Installation and Configuration
Hardware Installation.................................................................................................... 2-1
Module Configuration................................................................................................... 2-2
Direct Parallel Port Connection to PC............................................................ 2-3
Analog I/O Configuration............................................................................... 2-5
Analog Output Configuration .......................................................... 2-6
Analog Input Configuration ............................................................. 2-6
Input Mode ........................................................................ 2-6
RSE Input (Eight Channels, Factory Setting).................... 2-8
NRSE Input (Eight Channels) ........................................... 2-8
DIFF Input (Four Channels) .............................................. 2-8
Analog Input Polarity and Range Configuration ............................. 2-9
SCXI Configuration........................................................................................ 2-9
© National Instruments Corporation
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SCXI-1200 User Manual
Table of Contents
Chapter 3
Signal Connections
Front Connector............................................................................................................ 3-2
Front Connector Signal Connection Descriptions ......................................... 3-2
Analog Input Signal Connections .................................................................. 3-4
Types of Signal Sources................................................................................. 3-6
Floating Signal Sources ................................................................... 3-6
Ground-Referenced Signal Sources................................................. 3-6
Input Configurations ...................................................................................... 3-7
Differential Connection Considerations (DIFF Configuration) ...... 3-7
Differential Connections for Grounded Signal Sources .................. 3-8
Differential Connections for Floating Signal Sources..................... 3-9
Single-Ended Connection Considerations ....................................... 3-10
Single-Ended Connections for Floating Signal Sources (RSE Configuration)
3-11
Single-EndedConnectionsforGroundedSignalSources(NRSEConfiguration)
3-11
Common-Mode Signal Rejection Considerations ........................... 3-13
Analog Output Signal Connections................................................................ 3-13
Digital I/O Signal Connections........................................................ 3-14
Port C Pin Connections.................................................................... 3-17
Timing Specifications...................................................................... 3-17
Mode 1 Input Timing ........................................................ 3-19
Mode 1 Output Timing...................................................... 3-20
Mode 2 Bidirectional Timing............................................ 3-20
Timing Connections....................................................................................... 3-22
DAQ Timing Connections............................................................... 3-22
General-Purpose Timing Signal Connections and
General-Purpose Counter/Timer Signals........................ 3-26
Digital I/O Signal Connections for the SCXIbus ............................ 3-30
Chapter 4
Theory of Operation
Functional Overview .................................................................................................... 4-1
Analog Input and DAQ Circuitry ................................................................................. 4-2
Analog Input Circuitry ................................................................................... 4-3
DAQ Timing Circuitry .................................................................... 4-4
Single-Channel Data Acquisition...................................... 4-5
Multiple-Channel (Scanned) Data Acquisition ................. 4-5
DAQ Rates ........................................................................ 4-6
Analog Output Circuitry.............................................................................................. 4-8
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© National Instruments Corporation
Table of Contents
Digital I/O Circuitry...................................................................................................... 4-10
Timing I/O Circuitry ..................................................................................................... 4-11
SCXI Digital Interface .................................................................................................. 4-14
SCXI Scanning Modes ................................................................................... 4-15
Single-Module Parallel Scanning..................................................... 4-15
Multiple-Module Multiplexed Scanning.......................................... 4-15
Chapter 5
Calibration
Calibration at Higher Gains .......................................................................................... 5-2
Calibration Equipment Requirements........................................................................... 5-3
Using the Calibration Function..................................................................................... 5-3
Appendix A
Specifications
Appendix B
Installation Troubleshooting
Appendix C
Customer Communication
Glossary
Index
Figures
Figure 1-1.
The Relationship between the Programming Environment,
NI-DAQ, and Your Hardware ............................................................... 1-4
Figure 2-1.
SCXI-1200 Parts Locator Diagram........................................................ 2-4
Figure 3-1.
Figure 3-2.
Figure 3-3.
Figure 3-4.
Figure 3-5.
Figure 3-6.
SCXI-1200 Front Connector Pin Assignments...................................... 3-2
SCXI-1200 Instrumentation Amplifier.................................................. 3-5
Differential Input Connections for Grounded Signal Sources............... 3-8
Differential Input Connections for Floating Sources............................. 3-9
Single-Ended Input Connections for Floating Signal Sources .............. 3-11
Single-Ended Input Connections for Grounded Signal Sources............ 3-12
© National Instruments Corporation
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SCXI-1200 User Manual
Table of Contents
Figure 3-7.
Figure 3-8.
Figure 3-9.
Figure 3-10.
Figure 3-11.
Figure 3-12.
Figure 3-13.
Figure 3-14.
Figure 3-15.
Figure 3-16.
Figure 3-17.
Figure 3-18.
Figure 3-19.
Analog Output Signal Connections ....................................................... 3-14
Digital I/O Connections......................................................................... 3-16
Mode 1 Timing Specifications for Input Transfers ............................... 3-19
Mode 1 Timing Specifications for Output Transfers ............................ 3-20
Mode 2 Timing Specification for Bidirectional Transfers .................... 3-21
EXTCONV* Signal Timing .................................................................. 3-22
Posttrigger DAQ Timing Case 1 ........................................................... 3-23
Posttrigger DAQ Timing Case 2 ........................................................... 3-24
Pretrigger DAQ Timing......................................................................... 3-25
EXTUPDATE* Signal Timing for Updating DAC Output .................. 3-26
Event-Counting Application with External Switch Gating ................... 3-27
Frequency Measurement Application ................................................... 3-28
General-Purpose Timing Signals........................................................... 3-29
Figure 4-1.
Figure 4-2.
Figure 4-3.
Figure 4-4.
Figure 4-5.
Figure 4-6.
Figure 4-7.
Figure 4-8.
Figure 4-9.
Figure 4-10.
Figure 4-11.
SCXI-1200 Block Diagram ................................................................... 4-1
Analog Input and DAQ Circuitry Block Diagram ................................ 4-3
Analog Output Circuitry Block Diagram .............................................. 4-9
Digital I/O Circuitry Block Diagram..................................................... 4-10
Timing I/O Circuitry Block Diagram .................................................... 4-12
Two-Channel Interval-Scanning Timing............................................... 4-13
Single-Channel Interval Timing ............................................................ 4-14
Digital Interface Circuitry Block Diagram............................................ 4-14
Single-Module Parallel Scanning .......................................................... 4-15
Multiple-Module Multiplexed Scanning Diagram ................................ 4-16
SCXI Configurations ............................................................................. 4-17
Tables
Table 2-1.
Table 2-2.
Table 2-3.
Analog I/O Settings ............................................................................... 2-5
Analog Input Configurations for the SCXI-1200.................................. 2-7
Digital Signal Connections, Jumper Settings ........................................ 2-10
Table 3-1.
Table 3-2.
Recommended Input Configurations for Ground-Referenced
and Floating Signal Sources .................................................................. 3-7
Port C Signal Assignments.................................................................... 3-17
Table 4-1.
Table 4-2.
Table 4-3.
Table 4-4.
Analog Input Settling Time Versus Gain .............................................. 4-7
SCXI-1200 Maximum Recommended DAQ Rates .............................. 4-7
Bipolar Analog Input Signal Range Versus Gain ................................. 4-7
Unipolar Analog Input Signal Range Versus Gain ............................... 4-8
SCXI-1200 User Manual
viii
© National Instruments Corporation
About
This
Manual
This manual describes the electrical and mechanical aspects of the
SCXI-1200 module and contains information concerning its operation
and programming. The SCXI-1200 is a member of the National
Instruments Signal Conditioning eXtensions for Instrumentation
(SCXI) Series modules. The SCXI-1200 is a combination DAQ and
SCXI module that communicates with the PC through the parallel port.
Organization of This Manual
The SCXI-1200 User Manual is organized as follows:
•
Chapter 1, Introduction, describes the SCXI-1200; lists the
contents of your SCXI-1200 kit; describes the optional software,
optional equipment, and custom cables; and explains how to
unpack the SCXI-1200 kit.
•
Chapter 2, Installation and Configuration, describes how to install
the SCXI-1200 into the SCXI chassis and how to configure the
SCXI-1200.
•
Chapter 3, Signal Connections, describes the signal connections to
the SCXI-1200 via the SCXI-1200 front connector and rear signal
connector and includes specifications and connection instructions
for the SCXI-1200 connector signals.
•
Chapter 4, Theory of Operation, contains a functional overview of
the SCXI-1200 module and explains the operation of each
functional unit of the SCXI-1200.
•
Chapter 5, Calibration, discusses the calibration of the SCXI-1200.
•
Appendix A, Specifications, lists the specifications for the
SCXI-1200.
•
Appendix B, Installation Troubleshooting, contains installation
troubleshooting information.
•
Appendix C, Customer Communication, contains forms you can
use to request help from National Instruments or to comment on our
products.
© National Instruments Corporation
ix
SCXI-1200 User Manual
About This Manual
•
The Glossary contains an alphabetical list and description of terms
used in this manual, including abbreviations, acronyms, metric
prefixes, mnemonics, and symbols.
•
The Index contains an alphabetical list of key terms and topics in
this manual, including the page where you can find each one.
Conventions Used in This Manual
The following conventions appear in this manual:
<>
Angle brackets containing numbers separated by an ellipsis represent a
range of values associated with a bit or signal name (for example,
BDIO<3..0>).
bold italic
Bold italic text denotes a note, caution, or warning.
DIO board
DIO board refers to the National Instruments AT-DIO-32F,
MC-DIO-24, MC-DIO-32F, NB-DIO-24, NB-DIO-96, NB-DIO-32F,
PC-DIO 24, and PC-DIO-96 digital I/O DAQ boards unless otherwise
noted.
DIO-type
board
DIO-type board refers to National Instruments DAQ boards that have
only digital inputs and outputs. These boards include the DIO-24,
DIO-32F, and DIO-96 boards unless otherwise noted.
italic
Italic text denotes emphasis, a cross reference, or an introduction to a
key concept.
Lab board
Lab board refers to the National Instruments Lab-LC, Lab-NB, Lab-PC,
and Lab-PC+ boards unless otherwise noted.
MIO board
MIO board refers to the National Instruments AT-MIO-16,
AT-MIO-16D, AT-MIO-16F-5, AT-MIO-16X, AT-MIO-64F-5,
MC-MIO-16, NB-MIO-16, and NB-MIO-16X multichannel I/O DAQ
boards unless otherwise noted.
MIO-type
board
monospace
SCXI-1200 User Manual
MIO-type board refers to National Instruments DAQ boards that have
at least analog and digital inputs and outputs. These boards include the
MIO boards, the Lab boards, and the PC-LPM-16 board unless
otherwise noted.
Lowercase text in this font denotes text or characters that are to be
literally input from the keyboard, sections of code, programming
examples, and syntax examples. This font is also used for the proper
x
© National Instruments Corporation
About This Manual
names of disk drives, paths, directories, programs, subprograms,
subroutines, device names, functions, variables, filenames, and
extensions, and for statements and comments taken from program code.
SCXIbus
SCXIbus refers to the backplane in the chassis. A signal on the
backplane is referred to as the SCXIbus <signal name> line (or signal).
The SCXIbus descriptor may be omitted when the meaning is clear.
Slot 0
Slot 0 refers to the power supply and control circuitry in the SCXI
chassis.
The Glossary lists abbreviations, acronyms, metric prefixes,
mnemonics, symbols, and terms.
National Instruments Documentation
The SCXI-1200 User Manual is one piece of the documentation set for
your data acquisition and SCXI system. You can have any of several
types of manuals, depending on the hardware and software in your
system. Use the manuals you have as follows:
•
Getting Started with SCXI—This is the first manual you should
read. It gives an overview of the SCXI system and contains the
most commonly needed information for the modules, chassis, and
software.
•
Your SCXI hardware user manuals—Read these manuals next for
detailed information about signal connections and module
configuration. They also explain in greater detail how the module
works and contain application hints.
•
Your DAQ hardware user manuals—These manuals have detailed
information about the DAQ hardware that plugs into your
computer. Use these manuals for hardware installation and
configuration instructions, specification information about your
DAQ hardware, and application hints.
•
Software manuals—Examples of software manuals you may have
are the LabVIEW and LabWindows®/CVI documentation sets and
the NI-DAQ documentation. After you set up your hardware
system, use either the application software (LabVIEW or
LabWindows/CVI) or the NI-DAQ documentation to help you
write your application. If you have a large, complicated system, it
is worthwhile to look through the software manuals before you
configure your hardware.
© National Instruments Corporation
xi
SCXI-1200 User Manual
About This Manual
•
Accessory installation guides or manuals—If you are using
accessory products, read the terminal block and cable assembly
installation guides or accessory board user manuals. They explain
how to physically connect the relevant pieces of the system.
Consult these guides when you are making your connections.
•
SCXI Chassis User Manual—Read this manual for maintenance
information on the chassis and for installation instructions.
Related Documentation
The following National Instruments manual contains detailed
information for the register-level programmer.
•
SCXI-1200 Register-Level Programmer Manual
This manual is available from National Instruments by request. If you
are using NI-DAQ, LabVIEW, or LabWindows/CVI, you should not
need the register-level programmer manual. Using NI-DAQ, LabVIEW,
or LabWindows/CVI is as easy as using the low-level programming
described in the register-level programmer manual. Refer to Software
Programming Choices in Chapter 1, Introduction, of this manual to
learn more about your programming options.
Customer Communication
National Instruments wants to receive your comments on our products
and manuals. We are interested in the applications you develop with our
products, and we want to help if you have problems with them. To make
it easy for you to contact us, this manual contains comment and
configuration forms for you to complete. These forms are in
Appendix C, Customer Communication.
SCXI-1200 User Manual
xii
© National Instruments Corporation
Chapter
1
Introduction
This chapter describes the SCXI-1200; lists the contents of your
SCXI-1200 kit; describes the optional software, optional equipment,
and custom cables; and explains how to unpack the SCXI-1200 kit.
About the SCXI-1200
Thank you for buying the National Instruments SCXI-1200. The
SCXI-1200 is an SCXI module that works like the Lab-PC+
multifunction analog, digital, and timing I/O plug-in board. You can use
the SCXI-1200 in conjunction with other SCXI modules or as a standalone module. The SCXI-1200 module communicates with the PC
through the parallel port and works with the four-slot SCXI-1000, the
four-slot DC powered SCXI-1000DC, and the twelve-slot SCXI-1001
chassis.
With the SCXI-1200, you can use a Remote SCXI configuration with an
SCXI-2000 remote chassis or you can use either an SCXI-1000 chassis,
an SCXI-1001 chassis or an SCXI-1000 DC chassis outfitted with an
SCXI-2400 communications module. If you are using the second
option, you need to connect a serial port cable (either RS-232 or
RS-485) to the SCXI-2000 chassis or the SCXI-2400 module, and a
short parallel port cable from the SCXI-2000 or SCXI-2400 to the back
of the SCXI-1200 module. This short parallel port cable is included
with the SCXI-2000 remote chassis and the SCXI-2400 remote
communications module. As a stand-alone module, the SCXI-1200 has
eight analog input channels, that can be configured as eight singleended or four differential; a 12-bit successive-approximation ADC; two
12-bit DACs with voltage outputs; 24 lines of TTL-compatible digital
I/O; and 16-bit counter/timer channels for timing I/O.
The SCXI-1200 works with other National Instruments SCXI modules
and can operate in a single-chassis system. The SCXI-1200 controls the
operation of and digitizes the conditioned analog signals from other
SCXI modules.
© National Instruments Corporation
1-1
SCXI-1200 User Manual
Chapter 1
Introduction
The SCXI-1200 complies with IEEE 1284. This IEEE protocol supports
three different parallel port types—the original Centronics or
unidirectional port for printers, the PS2 type bidirectional port, and the
386-SL Enhanced Parallel Port (EPP).
A shielded terminal block, the SCXI-1302, has screw terminals for easy
signal attachment to the SCXI-1200.
With the SCXI-1200, the SCXI chassis can serve as a DAQ solution for
slotless computers, such as laptops, as well as PCs with parallel ports or
serial ports.
Detailed specifications of the SCXI-1200 are in Appendix A,
Specifications.
What You Need to Get Started
To set up and use your SCXI-1200, you will need the following:
❑ SCXI-1200 module
❑ SCXI-1200 User Manual
❑ One of the following software packages and documentation:
NI-DAQ for PC compatibles
LabVIEW for Windows
LabWindows/CVI
❑ Parallel port cable (1 m)
❑ Your computer
Note:
If you are using Remote SCXI, use the parallel port cable that is included
with the Remote SCXI unit.
Software Programming Choices
There are several options to choose from when programming your
National Instruments DAQ and SCXI hardware. You can use
LabVIEW, LabWindows/CVI, NI-DAQ, or register-level
programming.
SCXI-1200 User Manual
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© National Instruments Corporation
Chapter 1
Introduction
LabVIEW and LabWindows/CVI Application Software
LabVIEW and LabWindows/CVI are innovative program development
software packages for data acquisition and control applications.
LabVIEW uses graphical programming, whereas LabWindows/CVI
enhances traditional programming languages. Both packages include
extensive libraries for data acquisition, instrument control, data
analysis, and graphical data presentation.
LabVIEW features interactive graphics, a state-of-the-art user
interface, and a powerful graphical programming language. The
LabVIEW Data Acquisition VI Library, a series of VIs for using
LabVIEW with National Instruments DAQ hardware, is included with
LabVIEW. The LabVIEW Data Acquisition VI Library is functionally
equivalent to the NI-DAQ software.
LabWindows/CVI features interactive graphics, a state-of-the-art user
interface, and uses the ANSI standard C programming language. The
LabWindows/CVI Data Acquisition Library, a series of functions for
using LabWindows/CVI with National Instruments DAQ hardware, is
included with the NI-DAQ software kit. The LabWindows/CVI Data
Acquisition Library is functionally equivalent to the NI-DAQ software.
Using LabVIEW or LabWindows/CVI software will greatly reduce the
development time for your data acquisition and control application.
Note:
The DAQ interface for LabWindows for DOS does not support the use of
Remote SCXI.
NI-DAQ Driver Software
The NI-DAQ driver software is included at no charge with all National
Instruments DAQ hardware. NI-DAQ is not packaged with SCXI or
accessory products. NI-DAQ has an extensive library of functions that
you can call from your application programming environment. These
functions include routines for analog input (A/D conversion), buffered
data acquisition (high-speed A/D conversion), analog output (D/A
conversion), waveform generation (timed D/A conversion), digital I/O,
counter/timer operations, SCXI, RTSI, self-calibration, messaging, and
acquiring data to extended memory.
NI-DAQ has both high-level DAQ I/O functions for maximum ease of
use and low-level DAQ I/O functions for maximum flexibility and
performance. Examples of high-level functions are streaming data to
disk or acquiring a certain number of data points. An example of a
© National Instruments Corporation
1-3
SCXI-1200 User Manual
Chapter 1
Introduction
low-level function is writing directly to registers on the DAQ device.
NI-DAQ does not sacrifice the performance of National Instruments
DAQ devices because it lets multiple devices operate at their peak.
NI-DAQ also internally addresses many of the complex issues between
the computer and the DAQ hardware such as programming interrupts
and DMA controllers. NI-DAQ maintains a consistent software
interface among its different versions so that you can change platforms
with minimal modifications to your code. Whether you are using
conventional programming languages, LabVIEW, or
LabWindows/CVI, your application uses the NI-DAQ driver software,
as illustrated in Figure 1-1.
Conventional
Programming Environment
(PC, Macintosh, or
Sun SPARCstation)
LabVIEW
(PC, Macintosh, or
Sun SPARCstation)
LabWindows/CVI
(PC or Sun
SPARCstation)
NI-DAQ
Driver Software
Personal
Computer or
Workstation
DAQ or
SCXI Hardware
Figure 1-1. The Relationship between the Programming Environment,
NI-DAQ, and Your Hardware
Register-Level Programming
The final option for programming any National Instruments DAQ
hardware is to write register-level software. Writing register-level
SCXI-1200 User Manual
1-4
© National Instruments Corporation
Chapter 1
Introduction
programming software can be very time-consuming and inefficient, and
is not recommended for most users.
Even if you are an experienced register-level programmer, consider
using NI-DAQ, LabVIEW, or LabWindows/CVI to program your
National Instruments DAQ hardware. Using the NI-DAQ, LabVIEW, or
LabWindows/CVI software is easier than, and as flexible as,
register-level programming and can save you weeks of development
time.
Note:
If you are using the SCXI-1200 with Remote SCXI, you cannot do registerlevel programming.
Optional Equipment
You can use the following National Instruments products with your
SCXI-1200:
•
SCXI-1302 front terminal block
•
CB-50 I/O connector block
•
Type NB1 0.5 or 1.0 m ribbon cable
For more information about optional equipment available from
National Instruments, refer to your National Instruments catalogue or
call the office nearest you.
Custom Cables
The SCXI-1200 front signal connector is a 50-pin male ribbon-cable
header. The manufacturer part number of the header National
Instruments uses is as follows:
•
AMP Inc. (part number 1-103310-0)
The mating connector for the SCXI-1200 rear signal connector is a
50-position polarized ribbon-socket connector with strain relief.
National Instruments uses a polarized or keyed connector to prevent
inadvertent upside-down connection to the SCXI-1200.
Recommended manufacturer part numbers for this mating connector are
as follows:
•
Electronic Products Division/3M (part number 3425-7650)
•
T&B/Ansley Corporation (part number 609-5041CE)
© National Instruments Corporation
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SCXI-1200 User Manual
Chapter 1
Introduction
Standard 50-conductor 28 AWG stranded ribbon cables that work with
these connectors are as follows:
•
Electronic Products Division/3M (part number 3365/50)
•
T&B/Ansley Corporation (part number 171-50)
The SCXI-1200 rear connector (the parallel port connector) is the
standard 25-pin D-Subminiature. The manufacturer part number of the
connector National Instruments uses is as follows:
•
AMP Inc. (part number 747846-5)
The mating connector for the SCXI-1200 rear connector can be a
standard DB-25-style male connector.
Unpacking
Your SCXI-1200 module is shipped in an antistatic package to prevent
electrostatic damage to the module. Electrostatic discharge can damage
several components on the module. To avoid such damage in handling
the module, take the following precautions:
SCXI-1200 User Manual
•
Ground yourself via a grounding strap or by holding a grounded
chassis such as your SCXI chassis.
•
Touch the antistatic package to a metal part of your SCXI chassis
before removing the module from the package.
•
Remove the module from the package and inspect the module for
loose components or any other sign of damage. Notify National
Instruments if the module appears damaged in any way. Do not
install a damaged module into your SCXI chassis.
•
Never touch the exposed pins of connectors.
1-6
© National Instruments Corporation
Chapter
Installation and
Configuration
2
This chapter describes how to install the SCXI-1200 into the SCXI
chassis and how to configure the SCXI-1200.
The SCXI-1200 combines the functionality of plug-in DAQ boards and
SCXI modules. Previously, you connected the SCXI chassis with a
ribbon cable to a plug-in board in the PC. Any SCXI module in the
chassis could be used for this purpose. Now you can use the SCXI-1200
as a plug-in module that connects to the PC parallel port.
Hardware Installation
You can install the SCXI-1200 in any available SCXI chassis slot. After
you have made any necessary changes and have verified and recorded
the jumper setting on the form in Appendix C, Customer
Communication, you are ready to install the SCXI-1200. The following
are general installation instructions; consult your chassis user manual or
technical reference manual for specific instructions and warnings.
1.
Turn off the SCXI chassis. Do not insert the SCXI-1200 into a
chassis that is turned on.
2.
Insert the SCXI-1200 into the module guides. Gently guide the
module into the back of the slot until the connectors make contact.
3.
Screw the front mounting panel of the SCXI-1200 to the top and
bottom threaded strips of your SCXI chassis.
4.
If you are using Remote SCXI, connect the 25-pin DSUB end of the
short parallel port cable to the back of the SCXI-1200 and connect
the 36-pin end of the cable to the parallel port of the SCXI-2000
chassis or SCXI-2400 module adapter board. Then, connect a
serial port cable between the SCXI-2000 chassis or SCXI-2400
module adapter board and the serial port of your PC.
If you are not using Remote SCXI, connect one of the 25-pin
D SUB ends of the parallel port cable to the PC parallel port and the
other end to the back of the SCXI-1200. Screw in the mounting
screws on the connectors to establish a firm connection.
© National Instruments Corporation
2-1
SCXI-1200 User Manual
Chapter 2
Installation and Configuration
5.
If you are using Remote SCXI, set the desired baud rate and chassis
address by setting the DIP switches. For more information, refer to
the SCXI Chassis User Manual or the SCXI-2400 User Manual.
If you are using an SCXI-1000 chassis with jumper-selectable
addresses (Rev E or later) or and SCXI-1001 chassis, set the
jumpers to the desired chassis address.
6.
Visually verify the installation.
7.
Turn on the SCXI chassis.
8.
Turn on the computer or reconnect it to your chassis.
The SCXI-1200 board is installed. You are now ready to install and
configure your software.
If you are using NI-DAQ, refer to your NI-DAQ release notes. Find the
installation and system configuration section for your operating system
and follow the instructions given there.
If you are using LabVIEW, the software installation instructions are in
your LabVIEW release notes.
If you are using LabWindows/CVI, the software installation
instructions are in your LabWindows/CVI release notes.
If you are a register-level programmer, refer to the SCXI-1200
Register-Level Programmer Manual.
Module Configuration
The SCXI-1200 is software calibrated and software configurable.
Seven bits in the SCXI-1200 control registers configure all of the
analog I/O options. If you use NI-DAQ software, these bits are
automatically set or reset based on your configuration.
The SCXI-1200 has one reserved jumper, which selects the grounding
scheme for the SCXIbus guard. The parts locator diagram in Figure 2-1
shows the SCXI-1200 jumper (W1). If you are using Remote SCXI, you
do not need to allocate any PC hardware resources specifically for the
SCXI-1200 module. For more information on setting up your Remote
SCXI configuration, refer to the Getting Started with SCXI Manual, the
SCXI Chassis User Manual, or the SCXI-2400 User Manual.
SCXI-1200 User Manual
2-2
© National Instruments Corporation
Chapter 2
Installation and Configuration
Direct Parallel Port Connection to PC
An IBM-compatible PC can support up to three parallel printer ports,
which are designated LPT1, LPT2 and LPT3. Each port uses three
consecutive I/O addresses. When you boot your system, DOS assigns
the printer ports to the logical LPT designations, in the following order:
LPT1, LPT2, and LPT3. The starting addresses of the parallel printer
ports, in the order assigned to LPT designations, are 3BC, 378, and 278
hex. Therefore, if you have installed all three ports, 3BC hex is LPT1,
378 hex is LPT2, and 278 hex is LPT3. If you have not installed port
3BC hex, port 378 hex becomes LPT1 and port 278 hex becomes LPT2.
If only one parallel port is present, it is LPT1.
The SCXI-1200 uses the parallel port hardware interrupts for interruptdriven data acquisition. Interrupt channels 7 and 5 are commonly
allocated to parallel ports. Refer to your computer technical reference
manual for details about the parallel port base address and its interrupt
selection.
If you use the SCXI-1200 with NI-DAQ software, you select the port
and interrupt at configuration time.
The configuration utility displays on-screen all the parallel ports
addresses that were detected at boot-up. You must then select the port
address that you have connected to the SCXI-1200. You must also
select the interrupt level of the port. When you try to save these settings,
they will be tested and verified. Also, the type of parallel port
(Enhanced or Centronics) will be reported. If you incorrectly specify
the port address or interrupt, then an error will be reported. Refer to
Appendix B, Installation Troubleshooting, for tips on troubleshooting.
© National Instruments Corporation
2-3
SCXI-1200 User Manual
Chapter 2
Installation and Configuration
1
2
4
5
3
6
7
8
1
2
10
9
Front
1
2
3
4
Rear
Terminal Block Mounting Hole
Thumbscrew
Front Connector
Fuse
5
6
7
Rear Signal Connector
W1
SCXIbus Connector
8 Grounding Screw
9 Product Name, Assembly Number
10 Serial Number
Figure 2-1. SCXI-1200 Parts Locator Diagram
The following warnings contain important safety information
concerning hazardous voltages.
Warnings: KEEP AWAY FROM LIVE CIRCUITS. Do not remove equipment covers or
shields unless you are trained to do so. If signal wires are connected to the
module or terminal block, dangerous voltages may exist even when the
equipment is turned off. To avoid dangerous electrical shock, do not
perform procedures involving cover or shield removal unless you are
qualified to do so.
SCXI-1200 User Manual
2-4
© National Instruments Corporation
Chapter 2
Installation and Configuration
DO NOT OPERATE DAMAGED EQUIPMENT. The safety-protection features
built into this module can become impaired if the module becomes
damaged in any way. If it is damaged, turn the module off and do not use
it until service-trained personnel can check its safety. If necessary, return
the module to National Instruments for service and repair to ensure that its
safety is not compromised.
DO NOT SUBSTITUTE PARTS OR MODIFY EQUIPMENT. Because of the danger
of introducing additional hazards, do not install unauthorized parts or
modify the module. Return the module to National Instruments for service
and repair to ensure that its safety features are not compromised.
Analog I/O Configuration
The SCXI-1200 is shipped from the factory with the following
configuration:
•
Referenced single-ended input mode
•
±5 V analog input range (bipolar)
•
±5 V analog output range (bipolar)
Table 2-1 lists all the available analog I/O bit configurations for the
SCXI-1200 and shows the factory settings.
Table 2-1.
Parameter
© National Instruments Corporation
Analog I/O Settings
Configuration
Analog Output CH0 Polarity
Bipolar—±5 V (factory setting)
Unipolar—0 to 10 V
Analog Output CH1 Polarity
Bipolar—±5 V (factory setting)
Unipolar—0 to 10 V
Analog Input Range
Bipolar—±5 V (factory setting)
Unipolar—0 to 10 V
Analog Input Mode
Referenced single-ended (RSE)
(factory setting)
Non-referenced single-ended (NRSE)
Differential (DIFF)
Analog Bus 0 (SCXI)
2-5
SCXI-1200 User Manual
Chapter 2
Installation and Configuration
Both the analog input and analog output circuitries are software
configurable.
Analog Output Configuration
The SCXI-1200 has two channels of analog output voltage at the I/O
connector. You can configure each analog output channel for either
unipolar or bipolar output. A unipolar configuration has a range of 0 to
10 V at the analog output. A bipolar configuration has a range of -5 V
to +5 V at the analog output. In addition, you can select the coding
scheme for each DAC as either two’s complement or straight binary.
If you select a bipolar range for a DAC, the two’s complement coding
is recommended. In this mode, data values written to the analog output
channel range from F800 hex (-2,048 decimal) to 7FF hex (2,047
decimal). If you select a unipolar range for a DAC, the straight binary
coding is recommended. In this mode, data values written to the analog
output channel range from 0 to FFF hex (4,095 decimal).
Analog Input Configuration
Input Mode
The SCXI-1200 has three different input modes—referenced
single-ended (RSE) input, non-referenced single-ended (NRSE) input,
and differential (DIFF) input. The single-ended input configurations
use eight channels. The DIFF input configuration uses four channels.
Table 2-2 describes these configurations.
SCXI-1200 User Manual
2-6
© National Instruments Corporation
Chapter 2
Table 2-2.
Installation and Configuration
Analog Input Configurations for the SCXI-1200
Configuration
Description
RSE
Referenced single-ended configuration provides
eight single-ended inputs with the negative input
of the instrumentation amplifier referenced to
analog ground (factory setting).
NRSE
Non-referenced single-ended configuration
provides eight single-ended inputs with the
negative input of the instrumentation amplifier
tied to AISENSE/AIGND and not connected to
ground.
DIFF
Differential configuration provides four
differential inputs with the positive (+) input of
the instrumentation amplifier tied to channels 0,
2, 4, or 6 and the negative (-) input tied to
channels 1, 3, 5, or 7, respectively, thus choosing
channel pairs (0, 1), (2, 3), (4, 5), or (6, 7).
In addition, the input circuitry can select the SCXI Analog Bus 0 when
you are using the SCXI-1200 to sample data output by some other
module. On power-up, the AB0 bus is not selected. Refer to the
SCXI-1200 Register-Level Programmer Manual or your software
manual for details on how to use the multiplexed module mode. When
Analog Bus 0 is selected by the input circuitry, the DIFF mode is always
used. Analog Bus 0+ is tied to the positive (+) input of the
instrumentation amplifier. Analog Bus 0- is tied to the negative (-)
input of the instrumentation amplifier. In this case, the input mode
settings (RSE, NRSE, or DIFF) have no effect. However, the gain and
unipolar/bipolar settings are still valid.
While reading the following paragraphs, you may find it helpful to refer
to the Analog Input Signal Connections section of Chapter 3, Signal
Connections, which contains diagrams showing the signal paths for the
three configurations.
© National Instruments Corporation
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SCXI-1200 User Manual
Chapter 2
Installation and Configuration
RSE Input (Eight Channels, Factory Setting)
RSE input means that all input signals are referenced to a common
ground point that is also tied to the SCXI-1200 analog input ground.
The differential amplifier negative input is tied to analog ground. The
RSE configuration is useful for measuring floating signal sources. See
Types of Signal Sources in Chapter 3, Signal Connections, for more
information. With this input configuration, the SCXI-1200 can monitor
eight different analog input channels.
Considerations for using the RSE configuration are discussed in
Chapter 3, Signal Connections. Notice that in this mode, the return path
of the signal is analog ground, at the connector through the
AISENSE/AIGND pin.
NRSE Input (Eight Channels)
NRSE input means that all input signals are referenced to the same
common-mode voltage, which floats with respect to the SCXI-1200
analog ground. This common-mode voltage is subsequently subtracted
by the input instrumentation amplifier. The NRSE configuration is
useful for measuring ground-referenced signal sources.
Considerations for using the NRSE configuration are discussed in
Chapter 3, Signal Connections. Notice that in this mode, the return path
of the signal is through the negative terminal of the amplifier, at the
connector through the AISENSE/AIGND pin.
DIFF Input (Four Channels)
DIFF input means that each input signal has its own reference, and the
difference between each signal and its reference is measured. The
signal and its reference are each assigned an input channel. With this
input configuration, the SCXI-1200 can monitor four differential
analog input signals.
Considerations for using the DIFF configuration are discussed in
Chapter 3, Signal Connections. Notice that the signal return path is
through the negative terminal of the amplifier and through channel 1, 3,
5, or 7, depending on which channel pair you select.
These three modes are all software selectable.
SCXI-1200 User Manual
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© National Instruments Corporation
Chapter 2
Installation and Configuration
Analog Input Polarity and Range Configuration
You can select the analog input on the SCXI-1200 for either a unipolar
range (0 to 10 V) or a bipolar range (-5 to +5 V). The range and the
coding scheme are both software selectable. In addition, you can select
the coding scheme for analog input as either two’s complement or
straight binary. If you select a bipolar range, the two’s complement
coding is recommended. In this mode, -5 V input corresponds to F800
hex (-2,048 decimal) and +5 V corresponds to 7FF hex (2,047 decimal).
If you select a unipolar mode, the straight binary coding is
recommended. In this mode, 0 V input corresponds to 0 hex, and +10 V
corresponds to FFF hex (4,095 decimal).
Note:
If Analog Bus 0 is selected by the SCXI-1200, this selection is still valid. If
another module is in unipolar mode and drives Analog Bus 0, the
SCXI-1200 must also be in unipolar mode.
SCXI Configuration
The SCXI configuration circuitry is software configurable with the
configuration utility. There is also one jumper, as shown in Table 2-3.
When used in the stand-alone mode, the EXTCONV* and COUTB1
lines on the front connector can be driven with suitable signals for
causing external conversions and for interval scanning, respectively.
When used in conjunction with other modules (the SCXI mode), the
SCXI-1200 drives these pins with its own signals. These signals are
also routed through the SCXI bus and to other modules. The other
modules synchronize the switching of their input channels according to
these signals.
You use jumper J1 for grounding the SCXI guard to analog ground on
the SCXI-1200. The position of this jumper is shown in Table 2-3.
When used in stand-alone mode, this jumper should be in the default
(A-B) setting. When used in conjunction with other modules, the
jumper must be in the B-C setting.
Refer to the parts locator diagram in Figure 2-1 as you read the
following instructions. To configure this jumper, perform the following
steps:
1.
Remove the grounding screw of the top cover.
2.
Snap out the top cover of the shield by placing a screwdriver in the
groove at the bottom of the module.
© National Instruments Corporation
2-9
SCXI-1200 User Manual
Chapter 2
Installation and Configuration
3.
Remove the jumper and replace it on the appropriate pins.
4.
Snap the top cover back in place.
5.
Replace the grounding screw to ensure proper shielding.
Table 2-3 describes the jumper settings for different configurations.
Table 2-3.
Digital Signal Connections, Jumper Settings
Jumper W1 Settings
SCXI-1200 User Manual
A
NC
B
Guard
C
Guard
A
NC
B
Guard
C
Guard
2-10
Description
Position A-B (factory setting)—The
SCXI Analog Bus guard is not
connected to the SCXI-1200 analog
ground. When using the SCXI-1200
in stand-alone mode, use this setting.
Position B-C—The SCXI Analog
Bus guard is connected to the
SCXI-1200 analog ground. When
using the SCXI-1200 in conjunction
with other modules, use this setting.
© National Instruments Corporation
Chapter
3
Signal Connections
This chapter describes the signal connections to the SCXI-1200 module
via the SCXI-1200 front connector and rear signal connector and
includes specifications and connection instructions for the SCXI-1200
connector signals.
Warning: Connections that exceed any of the maximum ratings of input or output
signals on the SCXI-1200 can damage the SCXI-1200 module and the
computer. This includes connecting any power signals to ground and vice
versa. The description of each signal in this section includes information
about maximum input ratings. National Instruments is NOT liable for any
damages resulting from such signal connections.
© National Instruments Corporation
3-1
SCXI-1200 User Manual
Chapter 3
Signal Connections
Front Connector
Figure 3-1 shows the pin assignments for the SCXI-1200 front
connector. This connector is located on the front panel of the
SCXI-1200 module.
ACH0
ACH2
ACH4
ACH6
AISENSE/AIGND
AGND
DGND
PA1
PA3
PA5
PA7
PB1
PB3
PB5
PB7
PC1
PC3
PC5
PC7
EXTUPDATE*
OUTB0
OUTB1
CLKB1
GATB2
+5 V
1
3
5
7
9
2
4
6
8
10
ACH1
ACH3
11
13
15
17
19
21
23
25
27
29
31
33
35
37
39
41
43
45
47
49
12
14
16
18
20
22
24
26
28
30
32
34
36
38
40
42
44
46
48
50
DAC1OUT
ACH5
ACH7
DAC0OUT
PA0
PA2
PA4
PA6
PB0
PB2
PB4
PB6
PC0
PC2
PC4
PC6
EXTTRIG
EXTCONV*
GATB0
GATB1
OUTB2
CLKB2
DGND
Figure 3-1. SCXI-1200 Front Connector Pin Assignments
Front Connector Signal Connection Descriptions
The following table describes the connector pins on the SCXI-1200
front connector by pin number and gives the signal name and the
significance of each signal connector pin.
SCXI-1200 User Manual
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© National Instruments Corporation
Chapter 3
Pin
Signal Name
Signal Connections
Description
1-8
ACH<0..7>
Analog Channel—Analog Input channels 0 through 7
(single-ended).
9
AISENSE/AIGND
Analog Input Sense/Analog Input Ground—Analog input ground
in RSE mode, AISENSE in NRSE mode. Bidirectional.
10
DAC0OUT
Digital-to-Analog Converter 0 Output—Voltage output signal for
analog output channel 0.
11
AGND
Analog Ground—Analog output ground for analog output mode.
Analog input ground for DIFF or NRSE mode. Bidirectional.
12
DAC1OUT
Digital-to-Analog Converter 1 Output—Voltage output signal for
analog output channel 1.
13
DGND
Digital Ground—Bidirectional.
14-21
PA<0..7>
Port A 0 through 7—Bidirectional data lines for port A. PA7 is
the MSB, and PA0 is the LSB.
22-29
PB<0..7>
Port B 0 through 7—Bidirectional data lines for port B. PB7 is
the MSB, and PB0 is the LSB.
30-37
PC<0..7>
Port C 0 through 7—Bidirectional data lines for port C. PC7 is
the MSB, and PC0 is the LSB.
38
EXTTRIG
External Trigger—External control signal to start a timed
conversion sequence. Input.
39
EXTUPDATE*
External Update—External control signal to update DAC outputs.
Input.
40
EXTCONV*
External Convert—External control signal to trigger A/D
conversions when selected as input. Outputs conditioned
conversion pulse when selected as output. Bidirectional.
41
OUTB0
Counter B0 Output—Output.
42
GATB0
Counter B0 Gate—Input.
© National Instruments Corporation
3-3
SCXI-1200 User Manual
Chapter 3
Pin
Signal Connections
Signal Name
Description
43
OUTB1
Counter B1 Output—Counter B1 output used as HOLDTRIG for
SCXI use. Pulled high for user-driven interval scanning input
signal.
44
GATB1
Counter B1 Gate—Input.
45
CLKB1
Counter B1 Clock—Input (selectable).
46
OUTB2
Counter B2—Output.
47
GATB2
Counter B2 Gate—Input.
48
CLKB2
Counter B2 Clock—Input.
49
+5 V
+5 V output, fused at 1 A.
50
DGND
Digital Ground—Output.
*Indicates that the signal is active low.
The connector pins are grouped into analog input signal pins, analog
output signal pins, digital I/O signal pins, timing I/O signal pins and
SCXIbus control pins. Signal connection guidelines for each of these
groups are described in the following sections.
Analog Input Signal Connections
Pins 1 through 8 are analog input signal pins for the 12-bit ADC. Pin 9,
AISENSE/AIGND, is an analog common signal. You can use this pin
for a general analog power ground tie to the SCXI-1200 in RSE mode,
or as a return path in DIFF or NRSE mode. Pins 1 through 8 are tied to
the eight single-ended analog input channels of the input multiplexer
through 4.7 kΩ series resistances. Pins 2, 4, 6 and 8 are also tied to an
input multiplexer for DIFF mode.
The following input ranges and maximum ratings apply to inputs
ACH<0..7>:
•
•
SCXI-1200 User Manual
Input signal range
–
Bipolar input
±(5/gain) V
–
Unipolar input
0 to (10/gain) V
Maximum input voltage rating
3-4
±42 V powered on or off
© National Instruments Corporation
Chapter 3
Signal Connections
Warning: Exceeding the input signal range results in distorted input signals.
Exceeding the maximum input voltage rating may cause damage to the
SCXI-1200 module and to the computer. National Instruments is NOT
liable for any damages resulting from such signal connections.
How you connect analog input signals to the SCXI-1200 depends on
how you configure the SCXI-1200 analog input circuitry and the type
of input signal source. With different SCXI-1200 configurations, you
can use the SCXI-1200 instrumentation amplifier in different ways.
Figure 3-2 shows a diagram of the SCXI-1200 instrumentation
amplifier.
Instrumentation
Amplifier
+
Vin+
+
-
Vin-
Vm Measured
Voltage
-
Vm = [Vin+ - Vin-] * GAIN
Figure 3-2. SCXI-1200 Instrumentation Amplifier
The SCXI-1200 instrumentation amplifier applies gain, common-mode
voltage rejection, and high-input impedance to the analog input signals
connected to the SCXI-1200 module. Signals are routed to the positive
and negative inputs of the instrumentation amplifier through input
multiplexers on the SCXI-1200. The instrumentation amplifier
converts two input signals to a signal that is the difference between the
two input signals multiplied by the gain setting of the amplifier. The
amplifier output voltage is referenced to the SCXI-1200 ground. The
SCXI-1200 ADC measures this output voltage when it performs A/D
conversions.
© National Instruments Corporation
3-5
SCXI-1200 User Manual
Chapter 3
Signal Connections
All signals must be referenced to ground, either at the source device or
at the SCXI-1200. If you have a floating source, you must use a
ground-referenced input connection at the SCXI-1200. If you have a
grounded source, you must use a nonreferenced input connection at the
SCXI-1200.
Types of Signal Sources
When configuring the input mode of the SCXI-1200 and making signal
connections, you must first determine whether the signal source is
floating or ground referenced. These two types of signals are described
as follows.
Floating Signal Sources
A floating signal source is not connected in any way to the building
ground system but has an isolated ground-reference point. Some
examples of floating signal sources are outputs of transformers,
thermocouples, battery-powered devices, optical isolator outputs, and
isolation amplifiers. You must tie the ground reference of a floating
signal to the SCXI-1200 analog input ground to establish a local or
onboard reference for the signal. Otherwise, the measured input signal
varies or appears to float. An instrument or device that supplies an
isolated output falls into the floating signal source category.
Ground-Referenced Signal Sources
A ground-referenced signal source is connected in some way to the
building system ground and is therefore already connected to a common
ground point with respect to the SCXI-1200, assuming that the PC is
plugged into the same power system. Nonisolated outputs of
instruments and devices that plug into the building power system fall
into this category.
The difference in ground potential between two instruments connected
to the same building power system is typically between 1 mV and
100 mV but can be much higher if power distribution circuits are not
properly connected. The connection instructions that follow for
grounded signal sources eliminate this ground potential difference from
the measured signal.
SCXI-1200 User Manual
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© National Instruments Corporation
Chapter 3
Signal Connections
Input Configurations
You can configure the SCXI-1200 for one of three input modes—RSE,
NRSE, or DIFF. The following sections discuss the use of single-ended
and differential measurements, and considerations for measuring both
floating and ground-referenced signal sources. Table 3-1 summarizes
the recommended input configurations for both types of signal sources.
Table 3-1.
Recommended Input Configurations for Ground-Referenced
and Floating Signal Sources
Type of Signal
Recommended Input Configuration
Ground-Referenced
(nonisolated outputs,
plug-in instruments)
DIFF
NRSE
Floating
(batteries, thermocouples,
isolated outputs)
DIFF with bias resistors
RSE
Differential Connection Considerations
(DIFF Configuration)
Differential connections are those in which each SCXI-1200 analog
input signal has its own reference signal or signal return path. These
connections are available when you configure the SCXI-1200 in the
DIFF mode. Each input signal is tied to the positive input of the
instrumentation amplifier, and its reference signal, or return, is tied to
the negative input of the instrumentation amplifier.
When you configure the SCXI-1200 for DIFF input, each signal uses
two of the multiplexer inputs—one for the signal and one for its
reference signal. Therefore, only four analog input channels are
available when using the DIFF configuration. You should use the DIFF
input configuration when any of the following conditions are present:
•
Input signals are low level (less than 1 V).
•
Leads connecting the signals to the SCXI-1200 are greater than
15 ft.
•
Any of the input signals requires a separate ground-reference point
or return signal.
•
The signal leads travel through noisy environments.
© National Instruments Corporation
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SCXI-1200 User Manual
Chapter 3
Signal Connections
Differential signal connections reduce picked-up noise and increase
common-mode signal and noise rejection. With these connections,
input signals can float within the common-mode limits of the input
instrumentation amplifier.
Differential Connections for Grounded
Signal Sources
Figure 3-3 shows how to connect a ground-referenced signal source to
an SCXI-1200 module configured for DIFF input. Configuration
instructions are included in the Analog Input Configuration section in
Chapter 2, Installation and Configuration.
Grounded
Signal
Source
+
Vs
1
ACH0
3
ACH2
5
ACH4
7
ACH6
2
ACH1
+
-
CommonMode
Noise,
Ground
Potential,
and so on
+
+
-
4
ACH3
6
ACH5
8
ACH7
9
AISENSE/AIGND (not connected)
11
AGND
Vm
Measured
Voltage
-
Vcm
-
Front Connector
SCXI-1200 Module in DIFF Configuration
Figure 3-3. Differential Input Connections for Grounded Signal Sources
SCXI-1200 User Manual
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© National Instruments Corporation
Chapter 3
Signal Connections
With this type of connection, the instrumentation amplifier rejects both
the common-mode noise in the signal and the ground-potential
difference between the signal source and the SCXI-1200 ground (shown
as VCM in Figure 3-3).
Differential Connections for Floating Signal Sources
Figure 3-4 shows how to connect a floating signal source to a
SCXI-1200 module that is configured for DIFF input. Configuration
instructions are included in the Analog Input Configuration section of
Chapter 2, Installation and Configuration.
Floating
Signal
Source
+
Vs
1
ACH0
3
ACH2
5
ACH4
7
ACH6
2
ACH1
+
4
ACH3
Measured
Voltage
-
6
ACH5
8
ACH7
9
AISENSE/AIGND (not connected)
11
AGND
+
-
100 kΩ
Bias
Current
Return
Paths
100 kΩ
Front Connector
-
Vm
SCXI-1200 Module in DIFF Configuration
Figure 3-4. Differential Input Connections for Floating Sources
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Signal Connections
The 100 kΩ resistors shown in Figure 3-4 create a return path to ground
for bias currents of the instrumentation amplifier. If there is no return
path, the instrumentation amplifier bias currents charge stray
capacitances, resulting in uncontrollable drift and possible saturation in
the amplifier. Typically, values from 10 to 100 kΩ are used.
A resistor from each input to ground, as shown in Figure 3-4, provides
bias current return paths for an AC-coupled input signal.
If the input signal is DC-coupled, you need only the resistor that
connects the negative signal input to ground. This connection does not
lower the input impedance of the analog input channel.
Single-Ended Connection Considerations
Single-ended connections are those in which all SCXI-1200 analog
input signals are referenced to one common ground. The input signals
are tied to the positive input of the instrumentation amplifier, and their
common ground point is tied to the negative input of the
instrumentation amplifier.
When the SCXI-1200 is configured for single-ended input (NRSE or
RSE), eight analog input channels are available. You can use
single-ended input connections when the following criteria are met by
all input signals:
1.
Input signals are high level (greater than 1 V).
2.
Leads connecting the signals to the SCXI-1200 are less than 15 ft.
3.
All input signals share a common reference signal (at the source).
If any of the preceding criteria are not met, using DIFF input
configuration is recommended.
You can jumper configure the SCXI-1200 for two different types of
single-ended connections, RSE configuration and NRSE configuration.
Use the RSE configuration for floating signal sources; in this case, the
SCXI-1200 provides the reference ground point for the external signal.
Use the NRSE configuration for ground-referenced signal sources; in
this case, the external signal supplies its own reference ground point
and the SCXI-1200 should not supply one.
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Chapter 3
Signal Connections
Single-Ended Connections for Floating Signal
Sources (RSE Configuration)
Figure 3-5 shows how to connect a floating signal source to a
SCXI-1200 module configured for single-ended input. You must
configure the SCXI-1200 analog input circuitry for RSE input to make
these types of connections. Configuration instructions are included in
the Analog Input Configuration section of Chapter 2, Installation and
Configuration.
1
ACH0
2
ACH1
3
ACH2
8
ACH7
+
Floating
Signal
Source
Vs
+
9
+
AISENSE/AIGND
-
11
Measured
Voltage
Vm
AGND
-
Front Connector
SCXI-1200 Module in RSE Configuration
Figure 3-5. Single-Ended Input Connections for Floating Signal Sources
Single-Ended Connections for Grounded Signal
Sources (NRSE Configuration)
If you measure a grounded signal source with a single-ended
configuration, you must configure the SCXI-1200 in the NRSE input
configuration. The signal is connected to the positive input of the
SCXI-1200 instrumentation amplifier and the signal local ground
reference is connected to the negative input of the SCXI-1200
instrumentation amplifier. Therefore, you must connect the ground
© National Instruments Corporation
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SCXI-1200 User Manual
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Signal Connections
point of the signal to the AISENSE pin. Any potential difference
between the SCXI-1200 ground and the signal ground appears as a
common-mode signal at both the positive and negative inputs of the
instrumentation amplifier and is therefore rejected by the amplifier. On
the other hand, if the input circuitry of the SCXI-1200 is referenced to
ground, such as in the RSE configuration, this difference in ground
potentials appears as an error in the measured voltage.
Figure 3-6 shows how to connect a grounded signal source to a
SCXI-1200 module configured in the NRSE configuration.
Configuration instructions are included in the Analog Input
Configuration section in Chapter 2, Installation and Configuration.
GroundReferenced
Signal
Source
1
ACH0
2
ACH1
3
ACH2
8
ACH7
+
Vs
+
9
CommonMode
Noise
and so on
-
+
AISENSE/AIGND
11 AGND
Vcm
Vm
+
Measured
Voltage
-
-
Front Connector
SCXI-1200 Module in NRSA Input Configuration
Figure 3-6. Single-Ended Input Connections for Grounded Signal Sources
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Chapter 3
Signal Connections
Common-Mode Signal Rejection Considerations
Figures 3-3 and 3-6 show connections for signal sources that are
already referenced to some ground point with respect to the SCXI-1200.
In these cases, the instrumentation amplifier can reject any voltage
caused by ground-potential differences between the signal source and
the SCXI-1200. In addition, with differential input connections, the
instrumentation amplifier can reject common-mode noise pickup in the
leads connecting the signal sources to the SCXI-1200.
The common-mode input range of the SCXI-1200 instrumentation
amplifier is the magnitude of the greatest common-mode signal that can
be rejected.
The common-mode input range for the SCXI-1200 depends on the size
+
of the differential input signal (Vdiff = V in - V in) and the gain setting
of the instrumentation amplifier. In unipolar mode, the differential
input range is 0 to 10 V. In bipolar mode, the differential input range is
-5 to +5 V. Inputs should remain within a range of -5 to 10 V in both
bipolar and unipolar modes.
Analog Output Signal Connections
Pins 10 through 12 of the front connector are analog output signal pins.
Pins 10 and 12 are the DAC0OUT and DAC1OUT signal pins.
DAC0OUT is the voltage output signal for analog output channel 0.
DAC1OUT is the voltage output signal for analog output channel 1.
Pin 11, AGND, is the ground-reference point for both analog output
channels as well as analog input.
The following output ranges are available:
•
Output signal range
– Bipolar input
– Unipolar input
*Maximum load current
±5 V*
0 to 10 V*
± 5 mA for 12-bit linearity.
Figure 3-7 shows how to make analog output signal connections.
© National Instruments Corporation
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Chapter 3
Signal Connections
10
DAC0OUT
+
Load
Analog Output
Channel 0
VOUT 0
11
AGND
Load
VOUT 1
+
12
DAC1OUT
Analog Output
Channel 1
SCXI-1200 Module
Figure 3-7. Analog Output Signal Connections
Digital I/O Signal Connections
Pins 13 through 37 of the front connector are digital I/O signal pins.
Digital I/O on the SCXI-1200 uses the 82C55A integrated circuit. The
82C55A is a general-purpose peripheral interface containing 24
programmable I/O pins. These pins represent the three 8-bit ports
(PA, PB, and PC) of the 8255A.
Pins 14 through 21 are connected to the digital lines PA<0..7> for
digital I/O port A. Pins 22 through 29 are connected to the digital lines
PB<0..7> for digital I/O port B. Pins 30 through 37 are connected to
the digital lines PC<0..7> for digital I/O port C. Pin 13, DGND, is the
digital ground pin for all three digital I/O ports.
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Chapter 3
Signal Connections
The following specifications and ratings apply to the digital I/O lines.
•
Absolute maximum voltage input rating
–
+5.5 V with respect to DGND
–
-0.5 V with respect to DGND
•
Logical inputs and outputs
•
Digital I/O lines
Min
Max
0.8 V
–
Input logic low voltage
0V
–
Input logic high voltage
2.0 V
5.25 V
•
Output logic low voltage
(at output current = 1.7 mA)
0V
0.45 V
•
Output logic high voltage
(at output current = -200 µA)
•
Input load current
(0 < Vin < 5 V)
•
Darlington drive current
(REXT = 750 EXT = 1.5 V)
© National Instruments Corporation
3-15
2.4 V
5.0 V
-10.0 V
10.0 µA
-1.0 V
-4.0 mA
SCXI-1200 User Manual
Chapter 3
Signal Connections
Figure 3-8 illustrates signal connections for three typical digital I/O
applications.
+5 V
LED
Port A
14 PA0
PA<7..0>
Port B
22 PB0
PB<7..0>
TTL Signal
Port C
30 PC0
+5 V
PC<7..0>
Switch*
13
DGND
Front Connector
SCXI-1200 Module
*Complex switch circuitry is not shown in order to simplify the figure.
Figure 3-8. Digital I/O Connections
In Figure 3-8, port A is configured for digital output, and ports B and C
are configured for digital input. Digital input applications include
receiving TTL signals and sensing external device states such as the
switch in Figure 3-8. Digital output applications include sending TTL
signals and driving external devices such as the LED shown in
Figure 3-8.
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Chapter 3
Signal Connections
Port C Pin Connections
The signals assigned to port C depend on the mode in which the
82C55A is programmed. In mode 0, port C is considered to be two 4-bit
I/O ports. In modes 1 and 2, port C is used for status and handshaking
signals with two or three I/O bits mixed in. The following table
summarizes the signal assignments of port C for each programmable
mode. Refer to the SCXI-1200 Register-Level Programmer Manual for
programming information.
Table 3-2.
Programmable
Mode
Port C Signal Assignments
Group A
PC7
PC6
Group B
PC5
PC4
PC3
PC2
PC1
PC0
Mode 0
I/O
I/O
I/O
I/O
I/O
I/O
I/O
I/O
Mode 1 Input
I/O
I/O
IBFA
STBA*
INTRA
STBB*
IBFBB
INTRB
Mode 1
Output
OBFA*
ACKA*
I/O
I/O
INTRA
ACKB*
OBFB*
INTRB
Mode 2
OBFA*
ACKA*
IBFA
STBA*
INTRA
I/O
I/O
I/O
*Indicates that the signal is active low.
Timing Specifications
Use the handshaking lines STB* and IBF to synchronize input transfers.
Use the handshaking lines OBF* and ACK* to synchronize output
transfers.
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Signal Connections
The following signals are used in the timing diagrams shown later in
this chapter:
Name
Type
Description
STB*
Input
Strobe Input—A low signal on this handshaking line loads data into
the input latch.
IBF
Output
Input Buffer Full—A high signal on this handshaking line indicates
that data has been loaded into the input latch. This is primarily an
input acknowledge signal.
ACK*
Input
Acknowledge Input—A low signal on this handshaking line
indicates that the data written from the specified port has been
accepted. This signal is primarily a response from the external
device that it has received the data from the SCXI-1200.
OBF*
Output
Output Buffer Full—A low signal on this handshaking line indicates
that data has been written from the specified port.
INTR
Output
Interrupt Request—This signal becomes high when the 8255A is
requesting service during a data transfer. Set the appropriate
interrupt enable signals to generate this signal.
RD*
Internal
Read Signal—This signal is the read signal generated from the
control lines of the PC I/O channel.
WR*
Internal
Write Signal—This signal is the write signal generated from the
control lines of the PC I/O channel.
DATA
Bidirectional
Data Lines at the Specified Port—This signal indicates when the data
on the data lines at a specified port is or should be available.
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Chapter 3
Signal Connections
Mode 1 Input Timing
The timing specifications for an input transfer in mode 1 are as follows:
T1
T2
T4
STB *
T7
IBF
T6
INTR
RD *
T3
T5
DATA
Name
Description
Minimum
Maximum
T1
STB* pulse width
500
—
T2
STB* = 0 to IBF = 1
—
300
T3
Data before STB*= 1
0
—
T4
STB* = 1 to INTR = 1
—
300
T5
Data after STB*= 1
180
—
T6
RD* = 0 to INTR = 0
—
400
T7
RD* = 1 to IBF = 0
—
300
All timing values are in nanoseconds.
Figure 3-9. Mode 1 Timing Specifications for Input Transfers
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SCXI-1200 User Manual
Chapter 3
Signal Connections
Mode 1 Output Timing
The timing specifications for an output transfer in mode 1 are as
follows:
T3
WR*
T4
OBF*
T1
T6
INTR
T5
ACK*
DATA
T2
Name
Description
Minimum
Maximum
T1
WR* = 0 to INTR = 0
—
450
T2
WR* = 1 to output
—
350
T3
WR* = 1 to OBF* = 0
—
650
T4
ACK* = 0 to OBF* = 1
—
350
T5
ACK* pulse width
300
—
T6
ACK* = 1 to INTR = 1
—
350
All timing values are in nanoseconds.
Figure 3-10. Mode 1 Timing Specifications for Output Transfers
Mode 2 Bidirectional Timing
The timing specifications for bidirectional transfers in mode 2 are as
follows:
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Chapter 3
Signal Connections
T1
WR *
T6
OBF *
INTR
T7
ACK *
T3
STB *
T10
T4
IBF
RD *
T2
T5
T8
T9
DATA
Name
Description
Minimum
Maximum
T1
WR* = 1 to OBF* = 0
—
650
T2
Data before STB*= 1
0
—
T3
STB* pulse width
500
—
T4
STB* = 0 to IBF = 1
—
300
T5
Data after STB* = 1
180
—
T6
ACK* = 0 to OBF = 1
—
350
T7
ACK* pulse width
300
—
T8
ACK* = 0 to output
—
300
T9
ACK* = 1 to output float
20
250
T10
RD* = 1 to IBF = 0
—
300
All timing values are in nanoseconds.
Figure 3-11. Mode 2 Timing Specification for Bidirectional Transfers
© National Instruments Corporation
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SCXI-1200 User Manual
Chapter 3
Signal Connections
Timing Connections
Pins 38 through 48 of the front connector are connections for timing
I/O signals. The SCXI-1200 timing I/O uses two 82C53 counter/timer
integrated circuits. One circuit, designated 82C53(A), is used
exclusively for DAQ timing, and the other, 82C53(B), is available for
general use. Pins 38 through 40 carry external signals that you can use
for DAQ timing in place of the dedicated 82C53(A). These signals are
explained in the next section, DAQ Timing Connections. Pins 41
through 48 carry general-purpose timing signals from 82C53(B). These
signals are explained in the General-Purpose Timing Signal
Connections and General-Purpose Counter/Timer Signals section later
in this chapter.
DAQ Timing Connections
Each 82C53 counter/timer circuit has three counters. Counter 0 on the
82C53(A) counter/timer (referred to as A0) is a sample interval counter
in timed A/D conversions. Counter 1 on the 82C53(A) counter/timer
(referred to as A1) is a sample counter that works in conjunction with
counter 0 for data acquisition. These counters are not available for
general use. In addition to counter A0, you can use EXTCONV* to
externally time conversions. See the SCXI-1200 Register-Level
Programmer Manual for the programming sequence you need to enable
this input. Figure 3-12 shows the timing requirements for the
EXTCONV* input. An A/D conversion is initiated by a falling edge on
the EXTCONV*.
tw
VIH
EXTCONV*
tw 250 ns min
tw
VIL
A/D Conversion starts within
125 ns from this point
Figure 3-12. EXTCONV* Signal Timing
Another external control, EXTTRIG, can either start a DAQ sequence
or terminate an ongoing DAQ sequence, depending on the mode—
Hardware Trigger (HWTRIG) or Pretrigger (PRETRIG). These modes
are software selectable.
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© National Instruments Corporation
Chapter 3
Signal Connections
In the HWTRIG mode, EXTTRIG serves as an external trigger to start
a DAQ sequence. In this mode, posttrigger mode, the sample interval
counter is gated off until a rising edge is sensed on the EXTTRIG line.
External conversions, however, are enabled on the first rising edge of
EXTCONV*, following the rising edge on the EXTTRIG line. Further
transitions on the EXTTRIG line have no effect until a new DAQ
sequence is established.
Figures 3-13 and 3-14 illustrate two possible posttrigger DAQ timing
cases. In Figure 3-13, the rising edge on EXTTRIG is sensed when the
EXTCONV* input is high. Thus, the first A/D conversion occurs on the
second falling edge of EXTCONV*, after the rising edge on EXTTRIG.
In Figure 3-14, the rising edge on EXTTRIG is sensed when the
EXTCONV* input is low. In this case, the first A/D conversion occurs
on the first falling edge of EXTCONV*, after the rising edge on
EXTTRIG.
Notice that Figures 3-13 and 3-14 show a controlled acquisition mode
DAQ sequence; that is, sample counter A1 disables further A/D
conversions after the programmed count (3 in the examples shown in
Figures 3-13 and 3-14) expires. The counter is not loaded with the
programmed count until the first falling edge following a rising edge on
the clock input; therefore two extra conversion pulses are generated as
shown in Figures 3-13 and 3-14. You can also use EXTTRIG as an
external trigger in free-run acquisition mode.
tw
VIH
tw
EXTTRIG
VIL
tw 50 ns min
EXTCONV*
External
Conversions
Enabled
CONVERT
Count Value Written
Sample
Counter
X
X
3
2
1
0
Figure 3-13. Posttrigger DAQ Timing Case 1
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SCXI-1200 User Manual
Chapter 3
Signal Connections
tw
VIH
tw
EXTTRIG
tw 50 ns min
VIL
td 50 ns min
EXTCONV*
External
Conversions
Enabled
CONVERT
Count Gets Loaded
Sample
Counter
X
X
3
2
1
0
Figure 3-14. Posttrigger DAQ Timing Case 2
In the PRETRIG mode, EXTTRIG serves as a pretrigger signal. In
pretrigger mode, A/D conversions are enabled via software before a
rising edge is sensed on the EXTTRIG input. However, the sample
counter, counter A1, is not gated on until a rising edge is sensed on the
EXTTRIG input. Additional transitions on this line have no effect until
you initiate a new DAQ sequence. Conversions remain enabled for the
programmed count after the trigger; therefore, data can be acquired
before and after the trigger. Pretrigger mode works only in controlled
acquisition mode, that is, counter A1 is required to disable A/D
conversions after the programmed count expires. Thus, the maximum
number of samples acquired after the trigger is limited to 65,535. The
number of samples acquired before the trigger is limited only by the size
of the memory buffer available for data acquisition. Figure 3-15 shows
a pretrigger DAQ timing sequence. Notice that, because A1 is loaded
and armed, it allows exactly four pulses after the EXTTRIG pulses.
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Chapter 3
Signal Connections
tw
VIH
tw
EXTTRIG
VIL
tw 50 ns min
EXTCONV*
CONVERT
Sample
Counter
4
3
2
1
0
Figure 3-15. Pretrigger DAQ Timing
Because both pretrigger and posttrigger modes use EXTTRIG input,
you can only use one mode at a time.
You can use the OUTB1 pin to initiate timing intervals in the interval
acquisition modes. This is explained in detail in the Timing I/O
Circuitry section in Chapter 4, Theory of Operation.
You use the final external control signal, EXTUPDATE*, to externally
control updating the output voltage of the 12-bit DACs or to generate
an externally timed interrupt. There are two update modes, immediate
update and later update. In immediate update mode the analog output is
updated as soon as the value is written into the DAC. If you select the
later update mode, the corresponding DAC voltage is updated by a low
level on the EXTUPDATE* signal. Furthermore, if you enable interrupt
generation, an interrupt is generated whenever a rising edge is detected
on the EXTUPDATE* bit. Therefore, you can perform externally
timed, interrupt-driven waveform generation on the SCXI-1200.
Figure 3-16 illustrates a waveform generation timing sequence using
the EXTUPDATE* signal. Notice that the DACs are updated by a low
level on the EXTUPDATE* line. Any writes to the DAC data registers
while EXTUPDATE* is low therefore result in immediate update of the
DAC output voltages.
© National Instruments Corporation
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SCXI-1200 User Manual
Chapter 3
Signal Connections
In the following figures, DAC OUTPUT UPDATE is the pulse that
updates the analog output, CNTINT is the signal that interrupts the PC,
DACWRT is the signal that writes a new value to the DAC< and
TMRINTCLR is the signal that clears the interrupt.
EXTUPDATE*
text
DAC OUTPUT
UPDATE
CNTINT
DACWRT
text 50 ns min
Figure 3-16. EXTUPDATE* Signal Timing for Updating DAC Output
The following rating applies to the EXTCONV*, EXTTRIG and
EXTUPDATE* signals.
•
Absolute maximum voltage input rating
-0.5 to 7.0 V with
respect to DGND
General-Purpose Timing Signal Connections and
General-Purpose Counter/Timer Signals
The general-purpose timing signals include the GATE, CLK, and OUT
signals for the three 82C53(B) counters. The 82C53 counter/timers can
be used for general-purpose applications such as pulse and square wave
generation; event counting; and pulse-width, time-lapse, and frequency
measurement. For these applications, CLK and GATE signals are sent
to the counters, and the counters are programmed for various
operations. The single exception is counter B0, which has an internal
2 MHz clock.
You perform pulse and square wave generation by programming a
counter to generate a timing signal at its OUT output pin.
You perform event counting by programming a counter to count rising
or falling edges applied to any of the 82C53 CLK inputs. You can then
read the counter value to determine the number of edges that have
occurred. You can gate counter operation on and off during event
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© National Instruments Corporation
Chapter 3
Signal Connections
counting. Figure 3-17 shows connections for a typical event-counting
operation in which a switch is used to gate the counter on and off.
+5 V
4.7 kΩ
CLK
OUT
GATE
Switch*
Counter (from Group B)
Signal
Source
13
DGND
I/O Connector
SCXI-1200 Module
*Complex switch circuitry is not shown in order to simplify the figure.
Figure 3-17. Event-Counting Application with External Switch Gating
Pulse-width measurement is performed by level gating. The pulse you
want to measure is applied to the counter GATE input. The counter is
loaded with the known count and is programmed to count down while
the signal at the GATE input is high. The pulse width equals the counter
difference (loaded value minus read value) multiplied by the CLK
period.
Perform time-lapse measurement by programming a counter to be edge
gated. An edge is applied to the counter GATE input to start the
counter. You can program the counter to start counting after receiving
a low-to-high edge. The time lapse since receiving the edge equals the
counter value difference (loaded value minus read value) multiplied by
the CLK period.
© National Instruments Corporation
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SCXI-1200 User Manual
Chapter 3
Signal Connections
To perform frequency measurement, program a counter to be level
gated and count the number of falling edges in a signal applied to a CLK
input. The gate signal applied to the counter GATE input is of known
duration. In this case, you program the counter to count falling edges at
the CLK input while the gate is applied. The frequency of the input
signal then equals the count value divided by the gate period.
Figure 3-18 shows the connections for a frequency measurement
application. You can also use a second counter to generate the gate
signal in this application. In this case, program the second counter for a
one-shot mode. This scheme needs an external inverter to make the
output pulse of the second counter active high.
+5 V
4.7 kΩ
CLK
OUT
GATE
Signal
Source
Gate
Source
Counter
13
DGND
I/O Connector
SCXI-1200 Module
Figure 3-18. Frequency Measurement Application
The GATE, CLK, and OUT signals for counters B1 and B2 are available
at the I/O front connector. In addition, the GATE and CLK pins are
pulled up to +5 V through a 4.7 kΩ resistor.
The following specifications and ratings apply to the 82C53 I/O signals:
•
SCXI-1200 User Manual
Absolute maximum voltage input rating
3-28
-0.5 to 7.0 V with
respect to DGND
© National Instruments Corporation
Chapter 3
•
•
Signal Connections
82C53 digital input specifications (referenced to DGND):
–
V
–
V
–
Input load current
input logic high voltage
2.2 V minimum
input logic low voltage
0.8 V maximum
IH
IL
±10.0 µA maximum
82C53 digital output specifications (referenced to DGND):
–
V
–
V
–
I
–
I
OH
OL
OH
OL
output logic high voltage
2.4 V minimum
output logic low voltage
0.45 V maximum
output source current, at V
output sink current, at V
OH
OL
400.0 µA maximum
2.2 mA maximum
Figure 3-19 shows the timing requirements for the GATE and CLK
input signals and the timing specifications for the OUT output signals
of the 82C53.
tpwh
tsc
VIH
tpwl
CLK
VIL
tgh
tgsu
VIH
GATE
VIL
tgwh
tgwl
toutc
toutg
VOH
OUT
VOL
tsc
clock period
380 ns minimum
tpwh
clock high level
230 ns minimum
tpwl
clock low level
150 ns minimum
tgsu
gate setup time
100 ns minimum
tgh
gate hold time
50 ns minimum
tgwh
gate high level
150 ns minimum
tgwl
gate low level
100 ns minimum
toutg
output delay from clock
300 ns maximum
toutc
output delay from gate
400 ns maximum
Figure 3-19. General-Purpose Timing Signals
© National Instruments Corporation
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SCXI-1200 User Manual
Chapter 3
Signal Connections
The GATE and OUT signals in Figure 3-19 are referenced to the rising
edge of the CLK signal.
Digital I/O Signal Connections for the SCXIbus
When used with other SCXI modules, the SCXI-1200 communicates
with the SCXIbus by using some digital I/O lines. Four lines from
port B are used as outputs and one line of port C is used as input for
SCXIbus communication.
Pins 26 through 29, 31, 40, and 43 constitute the front signal connector
digital I/O lines that are used with the SCXIbus—the digital output
signals, the digital input signals, and the digital timing signals.
The digital input signal for SCXI is pin 31, SERDATIN, which is
equivalent to the SCXIbus signal MOSI.
The digital output signals for SCXI are pins 26, 27, 28, and 29. The
SCXI-1200 uses these pins to configure the SCXI module. Each digital
line emulates the SCXIbus communication signals as follows:
•
Pin 26, SERDATOUT, is equivalent to the SCXIbus MISO serial
data input line.
•
Pin 27, DAQD*/A, is equivalent to the SCXIbus D*/A line, and
indicates to the module whether the incoming serial stream on
SERDATIN is data (DAQD*/A = 0) or address (DAQD*/A = 1)
information.
•
Pin 28, SLOT0SEL*, is equivalent to the SCXIbus INTR* line, and
indicates whether the data on the SERDATIN line is being sent to
Slot 0 (SLOT0SEL* = 0) or to a module (SLOT0SEL* = 1).
•
Pin 29, SERCLK, is equivalent to the SCXIbus SPICLK line.
The digital timing signals (SCANCLK and HOLDTRIG) for SCXI are
sent out on pins 40 and 43.
•
Pin 40, SCANCLK, is equivalent to the SCXIbus TRIG0 line.
•
Pin 43, HOLDTRIG, is equivalent to the SCXIbus TRIG1 line.
If you use the SCXI-1200 for configuring the modules or Slot 0 of the
chassis in which it resides, then these signals are internally routed to the
SCXIbus. The signal that is driven by the SCXIbus (categorized as
input, above), as well as those driven by the DIO circuitry onto the
SCXIbus (categorized as outputs, above), appear on the corresponding
DIO pin on the connector.
SCXI-1200 User Manual
3-30
© National Instruments Corporation
Chapter 3
Signal Connections
If the SCXI-1200 programs another chassis through its 50-pin front
connector, then these DIO signals tap into the SCXIbus of the second
chassis. You must use an SCXI-1341, SCXI-1342, or SCXI-1344 cable
assembly for this purpose.
© National Instruments Corporation
3-31
SCXI-1200 User Manual
Chapter
4
Theory of Operation
This chapter contains a functional overview of the SCXI-1200 module
and explains the operation of each functional unit of the SCXI-1200.
Functional Overview
The block diagram in Figure 4-1 shows a functional overview of the
SCXI-1200 board.
16
12-Bit
A/D
FIFO
8
Input
Mux
12
Control
Signals
Parallel Port Interface
Parallel Port Connector
Decode
Circuitry
Pgm
Gain
Input
Mux
12
12-Bit
D/A
82C53
Ctr/Timer
Group A
82C53
Digital
Interface
1
Buffer
12
12-Bit
D/A
1
Front Panel Connector
Data/
Address
8
1 MHz
Timebase
SCXI
Control
Signals
÷10
10 MHz
Oscillator
82C53
Ctr/Timer
Group B
Buffer
Time
÷5
Divider
2 MHz
Timebase
Analog Bus 0
SCXIbus Connector
Figure 4-1. SCXI-1200 Block Diagram
The major components of the SCXI-1200 are as follows:
•
SCXIbus connector
•
Parallel port connector
© National Instruments Corporation
4-1
SCXI-1200 User Manual
Chapter 4
Theory of Operation
•
Analog input and DAQ circuitry
•
Analog output circuitry
•
Digital I/O and interface circuitry
•
Timing I/O circuitry
•
SCXI digital interface
You can execute DAQ functions by using the analog input circuitry and
some of the timing I/O circuitry. The internal data and control buses
interconnect the components.
The rest of the chapter explains the theory of operation of each of the
SCXI-1200 components. The theory of operation for the DAQ circuitry
is in the discussion of the analog input circuitry.
Analog Input and DAQ Circuitry
The SCXI-1200 has eight channels of analog input with softwareprogrammable gain and 12-bit A/D conversion. Using the timing
circuitry, the SCXI-1200 can also automatically time multiple A/D
conversions. Figure 4-2 shows a block diagram of the analog input and
DAQ circuitry.
In the following section, “stand-alone mode”, “parallel mode”, and
“single-module parallel scanning” are used interchangeably to indicate
a Lab-PC+ mode, in which there is no Slot 0 or multiple-module
multiplexed acquisition. The SCXI-1200 samples its input channels and
not Analog Bus 0 at all times.
SCXI-1200 User Manual
4-2
© National Instruments Corporation
Chapter 4
Theory of Operation
Data
Sampleand-Hold
Amp
ADC
Data
I/O Connector
GAIN2
Mux
MUX CTR CLK
ABO-
External Trigger
DAQ
Timing
CEXTCONV*
CEXTCONV*
Control
4
WR/RD
Address/Data
Counter/Timer
Signals
SCXIbus
Connector
MUX
Counter
CONVERT
3
AISENSE/
AIGND
EXTTRIG
8
Command
Registers
4
Status
5
GAIN1
ACH3
ACH5
ACH7
12
CONV
AVAIL
GAIN0
3
8
A/D
RD
Mux
ABO+
ACH1
A/D
FIFO
Parallel Port
Programmable
Gain Amp
Data
12
Parallel Port Interface
MUX
OUT
ACH0
ACH1
ACH2
ACH3
ACH4
ACH5
ACH6
ACH7
A/D
Data
Figure 4-2. Analog Input and DAQ Circuitry Block Diagram
You can operate the SCXI-1200 as a stand-alone module, in which it
samples its own input channels, or you can use the SCXI-1200 in
conjunction with other SCXI modules, in which case it samples Analog
Bus 0.
The stand-alone configuration is explained next. The latter
configuration, called SCXI mode, is explained in the SCXI Scanning
Modes section later in this chapter.
Analog Input Circuitry
The analog input circuitry consists of two analog input multiplexers, a
software-programmable gain amplifier, a 12-bit ADC, and a 12-bit
FIFO memory that is sign-extended to 16 bits.
One of the input multiplexers has eight analog input channels (channels
0 through 7). The other multiplexer is connected to channels 1, 3, 5, and
7 for differential mode. The input multiplexers provide input
overvoltage protection of ±45 V, powered on or off. In addition, you can
select the SCXI Analog Bus 0 as the input channel. Use software
© National Instruments Corporation
4-3
SCXI-1200 User Manual
Chapter 4
Theory of Operation
configuration to accomplish this whenever the SCXI-1200 is in the
SCXI mode and you have selected another module for signal
conditioning.
The programmable gain amplifier applies gain to the input signal,
allowing an input analog signal to be amplified before being sampled
and converted, thus increasing measurement resolution and accuracy.
The gain of the instrumentation amplifier is software selectable. The
SCXI-1200 board provides gains of 1, 2, 5, 10, 20, 50, and 100.
The SCXI-1200 uses a 12-bit successive-approximation ADC. The
12-bit resolution of the converter allows the converter to resolve its
input range into 4,096 different steps. This resolution also provides a
12-bit digital word that represents the value of the input voltage level
with respect to the converter input range. The ADC has an input range
of ±5 V and 0 to 10 V.
When an A/D conversion is complete, the ADC clocks the result into
the A/D FIFO. The A/D FIFO is 16 bits wide and 2 kwords deep. This
FIFO serves as a buffer to the ADC and provides two benefits. First,
when an A/D conversion is complete, the value is saved in the A/D
FIFO for later reading, and the ADC can start a new conversion.
Secondly, the A/D FIFO can collect up to 2 k A/D conversion values
before any information is lost, thus allowing software some extra time
to catch up with the hardware. If you store more than 2 k values in the
A/D FIFO without reading from the A/D FIFO, an error condition called
A/D FIFO overflow occurs and you lose A/D conversion information.
The output from the ADC can be interpreted as either straight binary or
two's complement, depending on which input mode you select (unipolar
or bipolar). In unipolar mode, the data from the ADC is interpreted as a
12-bit straight binary number with a range of 0 to +4,095. In bipolar
mode, the data from the ADC is interpreted as a 12-bit two's
complement number with a range of -2,048 to +2,047. In this mode, the
MSB of the ADC result is inverted to make it two's complement. The
output from the ADC is then sign-extended to 16 bits, causing either a
leading 0 or a leading F (hex) to be added, depending on the coding and
the sign. Thus, data values read from the FIFO are 16 bits wide.
DAQ Timing Circuitry
A DAQ operation refers to the process of taking a sequence of A/D
conversions with the sample interval (the time between successive A/D
conversions) carefully timed. The DAQ timing circuitry consists of
SCXI-1200 User Manual
4-4
© National Instruments Corporation
Chapter 4
Theory of Operation
various clocks and timing signals that perform this timing. The
SCXI-1200 board can perform both single-channel data acquisition and
multiple-channel (scanned) data acquisition in two modes—continuous
and interval. The SCXI-1200 uses a counter to switch between analog
input channels automatically during scanned data acquisition.
DAQ timing consists of signals that initiate a DAQ operation, initiate
individual A/D conversions, gate the DAQ operation, and generate
scanning clocks. Sources for these signals are supplied mainly by timers
on the SCXI-1200 board. One of the two 82C53 integrated circuits is
reserved for this purpose.
You can acquire data on a single channel or on multiple channels. In
either case, you can perform continuous or interval acquisition.
Single-Channel Data Acquisition
During single-channel data acquisition, the channel select and gain bits
in Command Register 1 select the gain and analog input channel before
data acquisition is initiated. These gain and multiplexer settings remain
constant during the entire DAQ process; therefore, you read all A/D
conversion data from a single channel. In addition, you can select the
SCXI Analog Bus 0 for data acquisition. This happens whenever
another module is selected and that module outputs its signal onto AB0.
In single-channel continuous acquisition mode, the SCXI-1200 samples
a single channel continuously without delays.
In single-channel interval acquisition mode, the SCXI-1200 samples a
single channel a programmable number of times, waits for the duration
of the scan interval, and repeats this cycle.
Multiple-Channel (Scanned) Data Acquisition
Multiple-channel data acquisition is performed by enabling scanning
during data acquisition. Multiple-channel scanning is controlled by a
scan counter.
For scanning operations, the scan counter decrements from the highest
numbered channel, which you specify, through channel 0, and then
repeats the sequence. Thus, you can scan any number of channels from
two to eight. Notice that you use the same gain setting for all channels
in the scan sequence.
© National Instruments Corporation
4-5
SCXI-1200 User Manual
Chapter 4
Theory of Operation
In scanned continuous acquisition mode, the SCXI-1200 scans the
selected channels repeatedly without delays and samples them.
In scanned-interval acquisition mode, the SCXI-1200 scans the selected
channels, waits for the duration of the scan interval, and repeats the
cycle.
DAQ Rates
Maximum DAQ rates (number of samples per second) are determined
by the conversion period of the ADC plus the sample-and-hold
acquisition time as well as any extra time required to transfer data back
to the PC. During multiple-channel scanning, the DAQ rates are further
limited by the settling time of the input multiplexers and programmable
gain amplifier. After the input multiplexers are switched, the amplifier
must be allowed to settle to the new input signal value to within 12-bit
accuracy before you perform an A/D conversion, or else 12-bit accuracy
will not be achieved. The settling time is a function of the gain selected.
Note:
If you are using Remote SCXI, the serial baud rate will affect the maximum
achievable DAQ rate. For more information, see Appendix A,
Specifications, in the SCXI Chassis User Manual.
The SCXI-1200 DAQ timing circuitry detects when DAQ rates are high
enough to cause A/D conversions to be lost. This happens if the
sampling interval is shorter than the conversion time for the ADC. If
this is the case, this circuitry sets an overrun error flag. If the
recommended DAQ rates in Table 4-2 are exceeded (an error flag is not
automatically set), the analog input circuitry may not perform at 12-bit
accuracy. If these rates are exceeded by more than a few microseconds,
A/D conversions may be lost. Table 4-1 shows the recommended
multiplexer and gain settling times for different gain settings. Table 4-2
shows the maximum recommended DAQ rates for both single-channel
and multiple-channel data acquisition. Notice that for a single-channel
data acquisition, the data can be acquired at the maximum rate at any
gain setting. This assumes that the input signal is band-limited. The
analog input bandwidth, however, is lower for higher gains. For
multiple-channel data acquisition, observing the DAQ rates in
Table 4-2 ensures 12-bit accuracy.
For short bursts of less than 2 ksamples, you can obtain a higher rate of
120 kS/s. This rate is limited only by the ADC conversion time, which
is specified at 8.33 µs.
SCXI-1200 User Manual
4-6
© National Instruments Corporation
Chapter 4
Table 4-1.
Theory of Operation
Analog Input Settling Time Versus Gain
Gain Setting
Settling Time Recommended
1, 2, 5, 10, 20, 50
18 µs typ, 25 µs guaranteed
100
40 µs
Table 4-2.
Acquisition
Mode
SCXI-1200 Maximum Recommended DAQ Rates
Gain
Setting
Rate
EPP Mode
Centronics Mode
Single
channel
1, 2, 5, 10,
20, 50, 100
100 kS/s
25 kS/s
Multiple
channel
1, 2, 5, 10,
20, 50
100
55.5 kS/s
25 kS/s
25 kS/s
25 kS/s
The recommended DAQ rates in Table 4-2 assume that voltage levels
on all the channels included in the scan sequence are within range for
the given gain and are driven by low-impedance sources. The signal
ranges for the possible gains are shown in Tables 4-3 and 4-4. Signal
levels outside the ranges shown in Table 4-3 on the channels included
in the scan sequence adversely affect the input settling time. Similarly,
you may need greater settling time for channels driven by highimpedance signal sources.
Table 4-3.
Bipolar Analog Input Signal Range Versus Gain
Gain Setting
© National Instruments Corporation
Input Signal Range
1
-5 V
to
4.99756 V
2
-2.5 V
to
2.49878 V
5
-1.0 V
to
0.99951 V
10
-500 mV
to
499.756 mV
20
-250 mV
to
249.877 mV
4-7
SCXI-1200 User Manual
Chapter 4
Theory of Operation
Table 4-3.
Bipolar Analog Input Signal Range Versus Gain (Continued)
Gain Setting
Input Signal Range
50
-250 mV
to
249.877 mV
100
-50 mV
to
49.975 mV
Table 4-4.
Unipolar Analog Input Signal Range Versus Gain
Gain Setting
Input Signal Range
1
0V
to
9.99756 V
2
0V
to
4.99878 V
5
0V
to
1.99951 V
10
0 mV
to
999.756 mV
20
0 mV
to
499.877 mV
50
0 mV
to
199.951 mV
100
0 mV
to
99.975 mV
Analog Output Circuitry
The SCXI-1200 has two channels of 12-bit D/A output. Each analog
output channel can provide unipolar or bipolar output. Figure 4-3 shows
a block diagram of the analog output circuitry.
SCXI-1200 User Manual
4-8
© National Instruments Corporation
Chapter 4
2SDAC0
Data
8
DAC0WRT
Status
Coding
DAC0
Data
DAC0OUT
Ref
5
8
AGND
4
5 V Internal
Reference
Ref
DAC1WRT
DAC1
I/O Connector
Control
11 Port Interface
Parallel Port
Theory of Operation
DAC1OUT
Coding
2SDAC1
Counter
A2
EXTUPDATE*
Command Register
CNFGWRT
2SDAC1
2SDAC0
2SDAC = 2’s Complement
Figure 4-3. Analog Output Circuitry Block Diagram
Each analog output channel contains a 12-bit DAC. The DAC in each
analog output channel generates a voltage proportional to the input Vref
multiplied by the digital code loaded into the DAC. You can load each
DAC with a 12-bit digital code by writing to the DAC0 (L and H) and
DAC1 (L and H) Registers on the SCXI-1200. The voltage output from
the two DACs is available at the SCXI-1200 I/O connector DAC0OUT
and DAC1OUT pins.
There are two ways you can upgrade the DAC voltages. In the first
mode, the DAC output voltage is updated as soon as you write to the
corresponding DAC Data Register. In the second mode, the DAC output
voltage does not change until a falling edge is detected either from
counter A2 or from EXTUPDATE*. These two modes are software
selectable.
You can program each DAC channel for either a unipolar voltage output
or a bipolar voltage output range. A unipolar output gives an output
voltage range of 0.0000 to +9.9976 V. A bipolar output gives an output
voltage range of -5.0000 to +4.9976 V. For unipolar output, 0.0000 V
© National Instruments Corporation
4-9
SCXI-1200 User Manual
Chapter 4
Theory of Operation
output corresponds to a digital code word of 0. For bipolar output,
-5.0000 V output corresponds to a digital code word of F800 hex.
One LSB is the voltage increment corresponding to a LSB change in the
digital code word. For both outputs, one LSB corresponds to:
10V
1 LSB = --------------4, 096
Digital I/O Circuitry
The digital I/O circuitry has an 82C55A integrated circuit. The 82C55A
is a general-purpose PPI containing 24 programmable I/O pins. These
pins represent the three 8-bit I/O ports (A, B, and C) of the 82C55A, as
well as PA<0..7>, PB<0..7>, and PC<0..7> on the SCXI-1200
I/O connector. Figure 4-4 shows a block diagram of the digital I/O
circuitry.
Data
8
Status
4
DIO RD/WRT
2
82C55A
Programmable
Peripheral
Interface
To Interrupt
Control
8
8
I/O Connector
5
Control
PB<0..7>
Parallel Port Interface
Parallel Port
PA<0..7>
DATA<0..7>
8
PC<0..7>
PC0
PC3
Figure 4-4. Digital I/O Circuitry Block Diagram
All three ports on the 82C55A are TTL-compatible. When enabled, the
digital output ports are capable of sinking 2.4 mA of current and
sourcing 2.6 mA of current on each digital I/O line. When the ports are
not enabled, the digital I/O lines act as high-impedance inputs.
SCXI-1200 User Manual
4-10
© National Instruments Corporation
Chapter 4
Theory of Operation
Timing I/O Circuitry
The SCXI-1200 uses two 82C53 counter/timer integrated circuits for
DAQ timing and for general-purpose timing I/O functions. One of these
is used internally for DAQ timing, and the other is available for general
use. Figure 4-5 shows a block diagram of both groups of timing I/O
circuitry (counter groups A and B).
© National Instruments Corporation
4-11
SCXI-1200 User Manual
Chapter 4
Theory of Operation
GATEB2
1 MHz Source
OUTB0
MUX
GATEB2
CLKB2
CLKB2
OUTB2
OUTB2
GATEB1
CLKB1
GATEB1
Scan
Interval/
General
Purpose
Counter
MUX
CCLKB1
CLKA0
N/C
OUTB1
OUTB0
GATEB0
Timebase
Extension/
General
Purpose
Counter
CTR RD
2 MHz
Source
CLKA0
CLKB0
CTR WR
Data
GATEA0
8253 Counter/Timer
Group B
Sample
Interval
Counter
I/O Connector
Parallel Port I/O Channel
MUX
OUTB0
GATEB0
COUTB1
OUTA0
MUX
8
CEXTCONV*
CLKA1
Sample
Counter
A/D Conversion Logic
GATEA1
EXTTRIG
OUTA1
CLKA2
+5 V
GATEA2
DAC
Timing
OUTA2
EXTUPDATE*
D/A Conversion Timing
8253 Counter/Timer
Group A
Figure 4-5. Timing I/O Circuitry Block Diagram
Each 82C53 contains three independent 16-bit counter/timers and one
8-bit Mode Register. As shown in Figure 4-5, counter group A is
reserved for DAQ timing, and counter group B is free for general use.
SCXI-1200 User Manual
4-12
© National Instruments Corporation
Chapter 4
Theory of Operation
The output of counter B0 can be used in place of the 1 MHz clock source
on counter A0 to allow clock periods greater than 65,536 µs.
The 82C53 for counter group A uses either a 1 MHz clock generated
from the onboard 10 MHz oscillator or the output from counter B0,
which has a 2 MHz clock source, for its timebase. Optionally, you can
use counter B1 to provide interval-scanning timing. In the intervalscanning mode, the CLK pin of counter B1 is driven by the same signal
that is driving CLKA0. The OUTB1 pin on the I/O connector initiates
scan sequences that are separated by a programmable scan interval time.
The timebases for counters B1 and B2 must be supplied externally
through the 50-pin I/O connector.
Figure 4-6 shows an example of interval-scanning timing.
Scan
Interval
OUTB1
Sample
Interval
Sample
Interval
OUTA0
GATEA0
ADC CH
CH1
CH0
CH1
CH0
CONVERT
Figure 4-6. Two-Channel Interval-Scanning Timing
The single-channel interval acquisition mode makes use of an
additional 8-bit counter, the interval counter. In this mode, counter B1
initiates scan sequences that are separated by a programmable interval
time. The interval counter is programmed for the number of samples of
the selected channel in each interval. Figure 4-7 shows an example of
single-channel interval timing. In this example, counter B1 is
programmed for the sample interval and the interval counter is
programmed to count three samples, wait for the duration of the scan
interval, count three samples, and so on. The acquisition operation ends
when the sample counter (counter A1) decrements to 0.
© National Instruments Corporation
4-13
SCXI-1200 User Manual
Chapter 4
Theory of Operation
Scan
Interval
OUTB1
Sample
Interval
Sample
Interval
OUTA0
CONVERT
GATEA0
Interval
Counter
Figure 4-7. Single-Channel Interval Timing
SCXI Digital Interface
SCXI Digital
Interface
8
Status
5
Control
Parallel Port
Data
5
RESET*
MISO
SPICLK
INTR*
D*/A
MOSI
SS*
SCXIbus
Digital Interface
TRIGHOLD
SCANCLK
SERDATIN
DAQD*/A
SLOTOSEL*
SERCLK
SERDATOUT
SERDATOUT
DAQD*/A
SLOT0SEL*
SERIALCLK
SCANCLK
HOLDTRIG
SERDATIN
50-Pin Front Connector
26
27
28
29
40
43
31
Parallel Port Interface
Figure 4-8 shows a diagram of the SCXI-1200 and SCXIbus digital
interface circuitry.
Figure 4-8. Digital Interface Circuitry Block Diagram
The circuitry is divided into an SCXI digital interface section and a rear
connector interface section.
SCXI-1200 User Manual
4-14
© National Instruments Corporation
Chapter 4
Theory of Operation
The SCXI digital interface buffers signals from the SCXIbus to the
module and drives signals from the module onto the SCXIbus.
The digital interface comprises the 82C55A programmable peripheral
interface along with buffers. All the SCXI control signals that tap into
the 82C55A DIO lines also appear on the 50-pin front connector. You
can program another chassis through the 50-pin front connector using
an SCXI-1341, SCXI-1342, or SCXI-1344 cable assembly.
SCXI Scanning Modes
The SCXI-1200 has two basic types of scanning modes—single-module
parallel scanning and multiple-module multiplexed scanning.
Single-Module Parallel Scanning
Single-module parallel scanning is the simplest scanning mode.
Figure 4-9 illustrates this mode. For more information about singlemodule parallel scanning, refer to the sections titled Single-Channel
Data Acquisition and Multiple-Channel (Scanned) Data Acquisition
earlier in this chapter.
SCXI-1000/1001
CH0
•
•
•
•
•
•
CH7
Analog
Input
MUX
SCXIbus
Analog
Input
Cicuitry
Parallel Port
SCXI-1200
Parallel
Port
Interface
Analog Bus 0
Figure 4-9. Single-Module Parallel Scanning
Multiple-Module Multiplexed Scanning
During multiplexed scanning, the SCXI-1200 provides the SCANCLK
signal to Slot 0 over the TRIG0 backplane line, and Slot 0 provides the
SCANCON signal to the modules. Slot 0 contains a module list FIFO
© National Instruments Corporation
4-15
SCXI-1200 User Manual
Chapter 4
Theory of Operation
(first-in first-out) memory chip, similar to the Channel/Gain FIFO on an
MIO-16 DAQ board, except that instead of having a channel number
and gain setting for each entry, it contains a slot number and a sample
count for each entry. The list in Slot 0 determines which module is
being accessed and for how many samples. It is important to make sure
that the lists on the DAQ board and Slot 0 are compatible so that the
samples are acquired as intended. Refer to your SCXI chassis manual
for more information.
In this mode, all the modules tie into Analog Bus 0 and are enabled
sequentially by SCANCON. Slot 0 must be programmed with the
sequence of modules and the number of samples per entry.
The SCXI-1200 sends SCANCLK onto TRIG0. Slot 0 counts these
SCANCLK pulses and selects the modules accordingly. When some
other module is selected, its output buffers are enabled by SCANCON,
so that Analog Bus 0 is driven by the output signal. At the same time,
Analog Bus 0 is selected by the SCXI-1200 for acquisition. When the
SCXI-1200 itself is chosen by Slot 0, the input muxes of the SCXI-1200
select the input channels on the front connector, depending on the bit
setting for channel selection and gains.
Figure 4-10 shows a block diagram of multiple-module multiplexed
scanning.
SCANCON X
SCXI-1000/1001
SCANCON B
SCANCON A
TRIG0
SCANCLK
SCXI-1200
Parallel Port
Slot 0
Slot A
Slot B
Slot X
Analog Bus 0
Figure 4-10. Multiple-Module Multiplexed Scanning Diagram
SCXI-1200 User Manual
4-16
© National Instruments Corporation
Chapter 4
Theory of Operation
You can configure the SCXI-1200 module in two ways—in a standalone mode or a multiple-module multiplexed mode. Figure 4-11a and
Figure 4-11b show both modes in standard configurations. Figure 4-11c
and Figure 4-11d illustrate Remote SCXI configurations.
SCXI-1000 Chassis
Parallel Cable
1200
Stand-Alone
PC
Slot 0
a. Configuration 1
SCXI-1000 Chassis
Parallel Cable
1200
PC
Multiplexed
Multiplexed
Multiplexed
Multiplexed
Slot 0
b. Configuration 2
SCXI-2000 Chassis
Serial Cable
Parallel
Cable
PC
1200
Stand-Alone or Multiplexed
Slot 0
c. Configuration 3
SCXI-1000 Chassis
Serial Cable
PC
Parallel
Cable
1200
Stand-Alone or Multiplexed
2400
Slot 0
d. Configuration 4
Figure 4-11. SCXI Configurations
© National Instruments Corporation
4-17
SCXI-1200 User Manual
Chapter 4
Theory of Operation
Note:
If the SCXI-1200 is in a chassis, then it must be the master module and
program Slot 0. To make the SCXI-1200 the master module, disconnect any
MIO or Lab Series plug-in boards that are connected to any other SCXI
modules in that chassis.
Refer to your SCXI-1000/1000DC/1001 Register-Level Programmer
Manual and the SCXI-1200 Register-Level Programmer Manual for
further details about programming.
SCXI-1200 User Manual
4-18
© National Instruments Corporation
Chapter
5
Calibration
This chapter discusses the calibration of the SCXI-1200. However, the
SCXI-1200 is factory calibrated, and National Instruments can
recalibrate your module if needed. To maintain the 12-bit accuracy of
the SCXI-1200 analog input and analog output circuitry, National
Instruments recommends that you recalibrate at six-month intervals.
There are three ways to perform calibrations.
•
Use the NI-DAQ Calibrate_1200 function. This is the easiest
way, because you do not need to know the details of the calibration
process.
•
Use the NI-DAQ functions to write to the calibration DACs and the
EEPROM.
•
Use your own register-level writes to the calibration DACs and the
EEPROM.
If you want to perform your own calibrations using the NI-DAQ
Calibrate_1200 function, go to the Using the Calibration Function
section later in this chapter. If you do not want to perform your own
calibrations, you can skip the remainder of this chapter.
To accomplish calibration using the last two methods, you need to know
the details of the calibration process. This information is in the
Calibration chapter of the SCXI-1200 Register-Level Programmer
Manual.
The SCXI-1200 is software calibrated, therefore there are no calibration
trimpots. The module is shipped with utility software for calibration.
The calibration process involves reading offset and gain errors from the
analog input and analog output sections and writing values to the
appropriate calibration DACs to null the errors. There are four
calibration DACs associated with the analog input section and four
calibration DACs associated with the analog output section, two for
each output channel. After the calibration process is complete, each
calibration DAC is at a known value. Because these values are lost
when the board is powered down, they are also stored in the onboard
EEPROM for future reference.
© National Instruments Corporation
5-1
SCXI-1200 User Manual
Chapter 5
Calibration
The factory information occupies one half of the EEPROM and is
protected. The lower half of the EEPROM contains user areas for
calibration data. There are eight different user areas.
When the SCXI-1200 is powered on, or the conditions under which it is
operating change, you should load the calibration DACs with values
from the EEPROM, or you can recalibrate the board. Calibration
software is included with the SCXI-1200 as part of the NI-DAQ
software.
If you use the SCXI-1200 with NI-DAQ and LabVIEW or
LabWindows/CVI and do not perform user calibration, the factory
calibration constants are loaded into the calibration DACs each time the
module is initialized. If you do perform user calibration, you can load
these user constants at startup. Therefore, the SCXI-1200 is calibrated
with the most recent constants each time you perform analog input or
output with the LabVIEW example VIs.
Calibration at Higher Gains
The SCXI-1200 has a maximum gain error of 0.5%. This means that if
the board is calibrated at a gain of 1, and if the gain is switched to 100,
a maximum of 50 mV error may result in the reading. If your application
can tolerate this error, then you do not have to recalibrate at that higher
gain. If this error is critical to your application, you should perform gain
calibration at all other gains (2, 5, 10, 20, 50, and 100), and store the
corresponding values in the other gain calibration data area. Using the
Calibrate_1200 function described later in this chapter, you can
specify the gain at which the SCXI-1200 operates, and the
corresponding value is loaded into the GAINCALDAC (analog input
gain calibration DAC) whenever any function related to the SCXI-1200
is called. Notice that at initialization the calibration constant for the
particular gain is loaded into the GAINCALDAC. This ensures a
maximum error of 0.02% at all gains. Also, the factory calibration area
contains gain calibration constants for all these gains.
SCXI-1200 User Manual
5-2
© National Instruments Corporation
Chapter 5
Calibration
Calibration Equipment Requirements
For best measurement results, calibrate the SCXI-1200 so that its
measurement accuracy is within ±0.012% of its input range (±0.5 LSB).
The equipment used to calibrate the SCXI-1200 should be 10 times as
accurate, that is, have ±0.001% rated accuracy. Calibration equipment
with four times the accuracy of the item under calibration is generally
considered acceptable. Four times the accuracy of the SCXI-1200 is
0.003%.
You need the following equipment to calibrate the SCXI-1200 module:
•
For analog input calibration, you need a precision variable DC
voltage source (usually a calibrator) with the following
specifications:
–
Accuracy
±0.001% standard
±0.003% sufficient
–
Range
Greater than ±10 V
–
Resolution
100 µV in ±10 V range (5 1/2 digits)
Using the Calibration Function
NI-DAQ contains the Calibrate_1200 function, with which you can
either load the calibration DACs with the factory constants or the
USERx constants, or perform your own calibration. To use the
Calibrate_1200 function, to perform calibration, you must ground an
analog input channel at the front connector (for offset calibration) and
apply an accurate voltage reference to another input channel (for gain
calibration). In addition, the DAC0 and DAC1 outputs must be wrapped
back and applied to two other analog input channels.
Specify the external voltage reference (for gain calibration) as one of
the parameters of the function. The other parameters are the number of
the input channel connected to AIGND (for pregain and postgain analog
input calibration) and the input channel numbers to which DAC0OUT
and DAC1OUT are fed back (for analog output calibration). Refer to the
NI-DAQ User Manual for PC Compatibles and the NI-DAQ Function
Reference Manual for PC Compatibles for more details on the
Calibrate_1200 function.
© National Instruments Corporation
5-3
SCXI-1200 User Manual
Appendix
A
Specifications
This appendix lists the specifications of the SCXI-1200. These
specifications are typical at 25° C unless otherwise stated. The
operating temperature range is 0° to 50° C.
Analog Input
Input Characteristics
Number of channels ............................Eight single-ended, four
differential, software selectable
Type of ADC ......................................Successive approximation
Resolution...........................................12 bits, 1 in 4,096
Conversion time
(including acquisition time) ................8.5 µs
Input signal ranges
Analog Input Signal
Gain (Software
Selectable)
© National Instruments Corporation
Analog Input Signal Ranges
(Software Selectable)
Bipolar
Unipolar
1
±5 V
0 to 10 V
2
±2.5 V
0 to 5 V
5
±1 V
0 to 2 V
10
±500 mV
0 to 1 V
20
±250 mV
0 to 500 mV
50
±100 mV
0 to 200 mV
100
±50 mV
0 to 100 mV
A-1
SCXI-1200 User Manual
Appendix A
Specifications
Input coupling .................................... DC
Max working voltage ......................... Input average should remain
within 7 V of ground
Overvoltage protection ....................... ±42 V powered on
±15 V powered off
Inputs protected ........................... ACH0..ACH7
FIFO buffer size ................................. 2,048 samples
Data transfers ..................................... Interrupts, programmed I/O
Minimum DAQ rate ........................... 1 sample every 35 minutes
Maximum sustained DAQ rates
(typ timing data observed in LabVIEW)
Acquisition
Mode
Gain
Setting
Rate
EPP
Mode
Centronics
Mode
Single
channel
1, 2, 5, 10,
20, 50, 100
100 kS/s
25 kS/s
Multiple
channel
1, 2, 5, 10
20
50
100
83.3 kS/s
62.5 kS/s
55.5 kS/s
25 kS/s
25 kS/s
25 kS/s
25 kS/s
25 kS/s
Transfer Characteristics
Relative accuracy (nonlinearity)......... ±0.5 LSB typ, ±1.5 LSB max
INL .................................................... ±0.5 LSB typ, ±1 LSB max
DNL ................................................... ±0.5 LSB typ, ±1 LSB max
No missing codes ............................... 12 bits, guaranteed
Offset error
After calibration, at all gains ....... ±(5 µV + 0.36 mV/gain) max
Before calibration, at all gains ..... ±(15 mV + 150 mV/gain) max
SCXI-1200 User Manual
A-2
© National Instruments Corporation
Appendix A
Specifications
Offset adjustment range ......................±37 mV max
Gain error
After calibration, at all gains ........0.020% of reading max
Before calibration
Gain = 1 ................................2% of reading max
Gain ≠1 with gain error
adjusted to 0 at gain = 1.........0.5% of reading max
Gain adjustment range ........................±25 mV max
Amplifier Characteristics
Input bias current ................................ 200 pA max
Input offset current ............................. 100 pA max
Input impedance .................................1006 Ω in parallel with 45 pF
CMRR
© National Instruments Corporation
Gain
CMRR DC to 60 Hz
1
60 dB
2
66 dB
5
74 dB
10 to 100
80 dB
A-3
SCXI-1200 User Manual
Appendix A
Specifications
Dynamic Characteristics
Analog input bandwidth
Gain
Single channel bandwidth
1 to 10
400 kHz
20
200 kHz
50
80 kHz
100
40 kHz
Settling time to full-scale step
Gain
Settling time to 0.012% (±0.5 LSB) accuracy
1
12 µs
2 to 50
16 µs typ, 18 µs max
100
40 µs
System noise (including quantization error)
Gain
Dither off
Dither on
1 to 50
0.3 LSB rms
0.6 LSB rms
100
0.6 LSB rms
0.8 LSB rms
Stability
Recommended warm-up time ...... 15 min
Offset temperature coefficient ..... ±(20 + 100/gain) µV°/ C
Gain temperature coefficient ....... ±50 ppm/°C
Explanation of Analog Input Specifications
Relative accuracy is a measure of the linearity of an ADC. However,
relative accuracy is a tighter specification than a nonlinearity
specification. Relative accuracy indicates the maximum deviation from
a straight line for the analog-input-to-digital-output transfer curve. If an
SCXI-1200 User Manual
A-4
© National Instruments Corporation
Appendix A
Specifications
ADC has been calibrated perfectly, then this straight line is the ideal
transfer function, and the relative accuracy specification indicates the
worst deviation from the ideal that the ADC permits.
A relative accuracy specification of ±1 LSB is roughly equivalent to
(but not the same as) a ±0.5 LSB nonlinearity or integral nonlinearity
specification because relative accuracy encompasses both nonlinearity
and variable quantization uncertainty, a quantity often mistakenly
assumed to be exactly ±0.5 LSB. Although quantization uncertainty is
ideally ±0.5 LSB, it can be different for each possible digital code and
is actually the analog width of each code. Thus, it is more specific to
use relative accuracy as a measure of linearity than it is to use what is
normally called nonlinearity, because relative accuracy ensures that the
sum of quantization uncertainty and A/D conversion error does not
exceed a given amount.
Integral nonlinearity in an ADC is an often ill-defined specification that
is supposed to indicate a converter’s overall A/D transfer linearity. The
manufacturer of the ADC chip used by National Instruments on the
DAQPad-1200 specifies its integral nonlinearity by stating that the
analog center of any code will not deviate from a straight line by more
than ±1 LSB. This specification is misleading because although a
particularly wide code’s center may be found within ±1 LSB of the
ideal, one of its edges may be well beyond ±1.5 LSB; thus, the ADC
would have a relative accuracy of that amount. National Instruments
tests its boards to ensure that they meet all three linearity specifications
defined in this appendix.
Differential nonlinearity is a measure of deviation of code widths from
their theoretical value of 1 LSB. The width of a given code is the size
of the range of analog values that can be input to produce that code,
ideally 1 LSB. A specification of ±1 LSB differential nonlinearity
ensures that no code has a width of 0 LSBs (that is, no missing codes)
and that no code width exceeds 2 LSBs.
System noise is the amount of noise seen by the ADC when there is no
signal present at the input of the board. The amount of noise that is
reported directly (without any analysis) by the ADC is not necessarily
the amount of real noise present in the system, unless the noise is
considerably greater than 0.5 LSB rms. Noise that is less than this
magnitude produces varying amounts of flicker, and the amount of
flicker seen is a function of how near the real mean of the noise is to a
code transition. If the mean is near or at a transition between codes, the
ADC flickers evenly between the two codes, and the noise is very near
© National Instruments Corporation
A-5
SCXI-1200 User Manual
Appendix A
Specifications
0.5 LSB. If the mean is near the center of a code and the noise is
relatively small, very little or no flicker is seen, and the noise reported
by the ADC as nearly 0 LSB. From the relationship between the mean
of the noise and the measured rms magnitude of the noise, the character
of the noise can be determined. National Instruments has determined
that the character of the noise in the DAQPad-1200 is fairly Gaussian,
so the noise specifications given are the amounts of pure Gaussian noise
required to produce our readings.
Explanation of Dither
The dither circuitry, when enabled, adds approximately 0.5 LSB rms of
white Gaussian noise to the signal to be converted to the ADC. This
addition is useful for applications involving averaging to increase the
resolution of the DAQPad-1200 to more than 12 bits, as in calibration.
In such applications, which are often lower frequency in nature, noise
modulation is decreased and differential linearity is improved by the
addition of the dither. For high-speed 12-bit applications not involving
averaging, dither should be disabled because it only adds noise.
When taking DC measurements, such as when calibrating the board,
enable dither and average about 1,000 points to take a single reading.
This process removes the effects of 12-bit quantization and reduces
measurement noise, resulting in improved resolution. Dither, or
additive white noise, has the effect of forcing quantization noise to
become a zero-mean random variable rather than a deterministic
function of input. For more information on the effects of dither, see
“Dither in Digital Audio” by John Vanderkooy and Stanley P. Lipshitz,
Journal of the Audio Engineering Society, Vol. 35, No. 12, Dec. 1987.
Explanation of DAQ Rates
Maximum DAQ rates (number of samples per second) are determined
by the conversion period of the ADC plus the sample-and-hold
acquisition time, which is specified at 8.5 µs. For single channel
sustained data acquisition, the maximum DAQ rate is limited by the
speed of the parallel port, 100 kS/s for EPP and 25 kS/s for Centronics,
and by the serial port baud rate if using Remote SCXI. During multiplechannel scanning, the DAQ rates are further limited by the settling time
of the input multiplexers and programmable gain amplifier. After the
input multiplexers are switched, the amplifier must be allowed to settle
to the new input signal value to within 12-bit accuracy. The settling
time is a function of the gain selected.
SCXI-1200 User Manual
A-6
© National Instruments Corporation
Appendix A
Specifications
Analog Output
Output Characteristics
Number of output channels .................Two single-ended
Resolution...........................................12 bits, 1 part in 4,096
Update rate (typ timing data
observed in LabVIEW) .......................8 kS/s in EPP mode, 4 kS/s
with standard Centronics port
Type of DAC ......................................Double-buffered
Data transfers......................................Interrupts, programmed I/O
Transfer Characteristics
Relative accuracy (INL)......................±0.25 LSB typ, ±0.50 LSB max
DNL....................................................±0.25 LSB typ, ±0.75 LSB max
Monotonicity ......................................12 bits, guaranteed
Offset error
After calibration ...........................±0.2 mV max
Before calibration.........................±50 mV max
Offset adjustment range, min ..............±37 mV
Gain error
After calibration ...........................0.004% of reading max
Before calibration.........................±1% of reading max
Gain adjustment range, min ................±100 mV
Voltage output
Ranges ................................................0 to +10 V, ±5 V,
software selectable
Output coupling ..................................DC
Output impedance ...............................0.2 Ω
© National Instruments Corporation
A-7
SCXI-1200 User Manual
Appendix A
Specifications
Current drive ...................................... ±2 mA
Protection ........................................... Short circuit to ground
Power-on state.................................... 0 V in bipolar mode, 5 V in
unipolar mode
Dynamic Characteristics
Settling time to 0.012% ...................... 6 µs for 10 V step
Slew rate ............................................ 10 V/µs
Offset temperature coefficient ............ ±60 µV/°C
Gain temperature coefficient .............. ±10 ppm/°C
Explanation of Analog Output Specifications
Relative accuracy in a D/A system is the same as nonlinearity because
no uncertainty is added due to code width. Unlike an ADC, every digital
code in a D/A system represents a specific analog value rather than a
range of values. The relative accuracy of the system is therefore limited
to the worst-case deviation from the ideal correspondence (a straight
line), excepting noise. If a D/A system has been calibrated perfectly,
then the relative accuracy specification reflects its worst-case absolute
error.
Differential nonlinearity in a D/A system is a measure of deviation of
code width from 1 LSB. In this case, code width is the difference
between the analog values produced by consecutive digital codes. A
specification of ±1 LSB differential nonlinearity ensures that the code
width is always greater than 0 LSBs (guaranteeing monotonicity) and is
always less than 2 LSBs.
Digital I/O
Number of channels ........................... 24
Compatibility ..................................... TTL
SCXI-1200 User Manual
A-8
© National Instruments Corporation
Appendix A
Specifications
Digital logic levels
Level
Min
Max
Input low voltage
- 0.3 V
0.8 V
Input high voltage
2.2 V
5.3 V
—
0.4 µA
Output high voltage (-2.5 mA)
3.7 V
—
Absolute max voltage
- 0.5 V
5.5 V
Output low voltage (2.5 mA)
Handshaking .......................................3 wire, 2 ports
Power-on state ....................................Inputs
Data Transfers ....................................Programmed I/O, interrupts
Timing I/O
Number of channels ............................Three 16-bit counter/timers
(uses two 82C53 STCs)
Resolution counter/timers ...................16 bits
Compatibility ......................................TTL, counter gate and clock
inputs are pulled up with 10 kΩ
resistors onboard.
Base clocks available ..........................2 MHz
Base clock accuracy ............................±0.01%
Max source frequency .........................8 MHz
Min source pulse duration ...................60 ns
Min gate pulse duration ......................50 ns
© National Instruments Corporation
A-9
SCXI-1200 User Manual
Appendix A
Specifications
Digital logic levels
Level
Min
Max
Input low voltage
- 0.3 V
0.8 V
Input high voltage
2.2 V
5.3 V
—
0.4 V
Output high voltage (-1 mA)
3.7 V
—
Absolute max voltage
- 0.5 V
5.5 V
Output low voltage (4 mA)
Parallel Port
Types ................................................. Compatible with Centronics and
Enhanced parallel port (EPP)
Throughput ........................................ 41 kBytes/s Centronics,
180 kBytes/s EPP
Power Requirement
+5 VDC.............................................. 50 mA
V+ DC................................................ 81 mA
V- DC ................................................ 40.25 mA
The SCXI-1000 chassis supplies a maximum of 200 mA current on the
5 V power supply and the SCXI-1001 supplies a minimum of 600 mA
on the 5 V power supply. Because the SCXI-1000 has four slots and the
SCXI-1001 has 12 slots, each module can draw a maximum of 200/4 or
600/12, which is 50 mA current on the 5 V line. However, if any slot is
unoccupied, other modules can use its share of the 50 mA. The +5 V on
the front connector can thus supply a current equal to 50 mA * (number
of unoccupied slots). This is the unused +5 V power. If all of the slots
are occupied, you must not use this +5 V to drive external circuitry. The
SCXI-1000 chassis is fused by a 1 A fuse, available from Allied
Electronics, part number 845-2007, or Littelfuse, part number 251001.
SCXI-1200 User Manual
A-10
© National Instruments Corporation
Appendix A
Specifications
Physical
Dimensions .........................................1.2 by 6.8 by 8.0 in.
(3 by 17.3 by 20.3 cm)
Connectors ..........................................50-pin male ribbon-cable front
connector
25-pin female Centronics type B
rear connector
Environment
Operating temperature ........................0° to 70° C
Storage temperature ............................-55° to 150° C
Relative humidity ...............................5% to 90% noncondensing
© National Instruments Corporation
A-11
SCXI-1200 User Manual
Appendix
Installation Troubleshooting
B
This appendix contains installation troubleshooting information.
1.
The NI-DAQ Configuration Utility reports an error when I try to
save the settings.
Check the following items if you receive this message:
“WDAQCONF could not find the device being configured on
the LPT at address 0xXXX. Check your LPT base address and
your LPT connections and retry.”
Note:
a.
Make sure your chassis is switched on and the screws of the
cable are tightly fastened.
b.
Check that your base address is correct. This can be done
either by checking your computer technical manual or, in some
cases, by checking the base address jumper. In Windows
applications, you may have a Hardware Control panel that will
allow you to enable and disable the parallel port. Common
parallel port addresses are 0x378, 0x278, 0x3BC, 0x280, and
0x290.
If your parallel port address does not appear under the Base Addr window
in WDAQCONF, you must turn off the Auto Test option under the Options
menu in the main window to access the other parallel port addresses.
© National Instruments Corporation
c.
Check that you are using the included 1 m parallel port cable.
If you suspect that you have a bad parallel port cable, replace
with a new cable or one that you know works with another
peripheral. If you are using another parallel port cable, check
to make sure it meets the required specifications (see the note
under item 2b).
d.
If you are still having problems, please report the computer
make and model number to National Instruments. If you have
a noncompatible parallel port and you have an available slot for
a plug-in board, try using the Far Point EPP card described in
the Optional Equipment section of Chapter 1, Introduction.
B-1
SCXI-1200 User Manual
Appendix B
Installation Troubleshooting
Check the following items if you receive this message:
“The device is not responding to the selected interrupt (IRQA).
If the IRQ on your board is jumper configurable, make sure
that the jumper settings correspond to the interrupt you have
selected. If they do, you will have to try a different interrupt
level.”
a.
Note:
If either IRQ level 7 or 5 are unselectable under the IRQ menu in
WDAQCONF, then another National Instruments board is using this
interrupt. You will have to free the appropriate IRQ level to allocate it for
your parallel port.
b.
Note:
SCXI-1200 User Manual
You may have an interrupt conflict with a non-National
Instruments device. If you have installed a PCMCIA card or a
plug-in board, you will have to ensure that IRQ5 or IRQ7 have
not been allocated for these devices.
For some PCMCIA cards installed with Cardware, it may be possible to
exclude your parallel port interrupt level by including the line XIRQ=7,
E for IRQ 7 or XIRQ=5, E for IRQ 5 in the cardware.ini file.
2.
Note:
IRQ levels 7 and 5 are the most common interrupt levels
reserved for the parallel port. Try saving your configuration
for both IRQ7 and IRQ5.
c.
You may have an interrupt conflict with a Windows-based
application. You will have to ensure that IRQ5 or IRQ7 have
not been allocated for this application. One place to search is
your system.ini file under Windows.
d.
If you are still having problems, please report the computer
make and model number to National Instruments.
The configuration utility works fine when I use a 1 m parallel port
cable but reports an error when I try to use a longer parallel port
cable.
a.
Ensure that your parallel port cable meets the required
specifications. (See the note under item 2b.)
b.
You may have to use a unidirectional parallel port extender in
order to achieve long distance solutions (one such extender is
made by BRAVO Communications). Your parallel port will be
recognized as a Centronics port with this extender.
National Instruments does not guarantee functionality with parallel port
cables longer than 1 m.
B-2
© National Instruments Corporation
Appendix B
3.
Note:
Installation Troubleshooting
I have an EPP port, but the configuration utility reports that I have
a Centronics port when I try to save the configuration settings.
a.
You may have to enable your parallel port as an EPP port.
Check for such utilities and ensure that your port is configured
for EPP.
b.
It is possible that your EPP port does not meet the EPP
specifications as given by the 1284 IEEE parallel port
specifications. In this case, your parallel port will be treated as
a Centronics port.
Your parallel port cable should meet the following specifications:
•
Characteristic unbalanced impedance of each signal and ground
pair of 62 Ω ±6 Ω, 4 to 16 MHz
•
Unbalanced capacitance of each cable pair less than 107 pF/m at
1 MHz
•
DC resistance of each cable wire of less than 0.22 Ω/m
•
Total propagation of each cable wire of less than 150 ns
© National Instruments Corporation
B-3
SCXI-1200 User Manual
Appendix
Customer Communication
C
For your convenience, this appendix contains forms to help you gather the information necessary
to help us solve your technical problems and a form you can use to comment on the product
documentation. When you contact us, we need the information on the Technical Support Form and
the configuration form, if your manual contains one, about your system configuration to answer
your questions as quickly as possible.
National Instruments has technical assistance through electronic, fax, and telephone systems to
quickly provide the information you need. Our electronic services include a bulletin board service,
an FTP site, a FaxBack system, and e-mail support. If you have a hardware or software problem,
first try the electronic support systems. If the information available on these systems does not
answer your questions, we offer fax and telephone support through our technical support centers,
which are staffed by applications engineers.
Electronic Services
Bulletin Board Support
National Instruments has BBS and FTP sites dedicated for 24-hour support with a collection of
files and documents to answer most common customer questions. From these sites, you can also
download the latest instrument drivers, updates, and example programs. For recorded instructions
on how to use the bulletin board and FTP services and for BBS automated information, call (512)
795-6990. You can access these services at:
United States: (512) 794-5422
Up to 14,400 baud, 8 data bits, 1 stop bit, no parity
United Kingdom: 01635 551422
Up to 9,600 baud, 8 data bits, 1 stop bit, no parity
France: 1 48 65 15 59
Up to 9,600 baud, 8 data bits, 1 stop bit, no parity
FTP Support
To access our FTP site, log on to our Internet host, ftp.natinst.com, as anonymous and use
your Internet address, such as [email protected], as your password. The support files
and documents are located in the /support directories.
© National Instruments Corporation
C-1
SCXI-1200 User Manual
FaxBack Support
FaxBack is a 24-hour information retrieval system containing a library of documents on a wide
range of technical information. You can access FaxBack from a touch-tone telephone at
(512) 418-1111.
E-Mail Support (currently U.S. only)
You can submit technical support questions to the appropriate applications engineering team
through e-mail at the Internet addresses listed below. Remember to include your name, address,
and phone number so we can contact you with solutions and suggestions.
GPIB: [email protected]
DAQ: [email protected]
VXI: [email protected]
LabWindows: [email protected]
LabVIEW: [email protected]
Lookout: [email protected]
HiQ: [email protected]
VISA: [email protected]
Fax and Telephone Support
National Instruments has branch offices all over the world. Use the list below to find the technical
support number for your country. If there is no National Instruments office in your country,
contact the source from which you purchased your software to obtain support.
Telephone
Australia
Austria
Belgium
Canada (Ontario)
Canada (Quebec)
Denmark
Finland
France
Germany
Hong Kong
Israel
Italy
Japan
Korea
Mexico
Netherlands
Norway
Singapore
Spain
Sweden
Switzerland
Taiwan
U.K.
03 9879 5166
0662 45 79 90 0
02 757 00 20
905 785 0085
514 694 8521
45 76 26 00
09 527 2321
01 48 14 24 24
089 741 31 30
2645 3186
03 5734815
02 413091
03 5472 2970
02 596 7456
5 520 2635
0348 433466
32 84 84 00
2265886
91 640 0085
08 730 49 70
056 200 51 51
02 377 1200
01635 523545
Fax
03 9879 6277
0662 45 79 90 19
02 757 03 11
905 785 0086
514 694 4399
45 76 26 02
09 502 2930
01 48 14 24 14
089 714 60 35
2686 8505
03 5734816
02 41309215
03 5472 2977
02 596 7455
5 520 3282
0348 430673
32 84 86 00
2265887
91 640 0533
08 730 43 70
056 200 51 55
02 737 4644
01635 523154
Technical Support Form
Photocopy this form and update it each time you make changes to your software or hardware, and
use the completed copy of this form as a reference for your current configuration. Completing this
form accurately before contacting National Instruments for technical support helps our
applications engineers answer your questions more efficiently.
If you are using any National Instruments hardware or software products related to this problem,
include the configuration forms from their user manuals. Include additional pages if necessary.
Name __________________________________________________________________________
Company _______________________________________________________________________
Address ________________________________________________________________________
_______________________________________________________________________________
Fax (___ )___________________ Phone (___ ) ________________________________________
Computer brand ________________ Model ________________ Processor___________________
Operating system (include version number) ____________________________________________
Clock speed ______MHz RAM _____MB
Mouse ___yes ___no
Display adapter __________________________
Other adapters installed _______________________________________
Hard disk capacity _____MB
Brand _____________________________________________
Instruments used _________________________________________________________________
_______________________________________________________________________________
National Instruments hardware product model __________ Revision ______________________
Configuration ___________________________________________________________________
National Instruments software product ____________________________ Version ____________
Configuration ___________________________________________________________________
The problem is: __________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
List any error messages: ___________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
The following steps reproduce the problem:____________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
SCXI-1200 Hardware and Software
Configuration Form
Record the settings and revisions of your hardware and software on the line to the right of each
item. Complete a new copy of this form each time you revise your software or hardware
configuration, and use this form as a reference for your current configuration. Completing this
form accurately before contacting National Instruments for technical support helps our
applications engineers answer your questions more efficiently.
National Instruments Products
Interrupt level of SCXI-1200 ____________________________________________________
Analog Output Channel 0 Configuration ___________________________________________
(Factory Setting—Bipolar)
Analog Output Channel 1 Configuration ___________________________________________
(Factory Setting—Bipolar)
Analog Input Configuration _____________________________________________________
(Factory Setting—Bipolar)
NI-DAQ or LabWindows/CVI version _____________________________________________
Other Products
Microprocessor _______________________________________________________________
Clock frequency _______________________________________________________________
Computer make and model ______________________________________________________
Type of video board installed ____________________________________________________
Operating system _____________________________________________________________
Operating system version _______________________________________________________
Programming language _________________________________________________________
Programming language version __________________________________________________
Other boards in system _________________________________________________________
Base I/O address of other boards _________________________________________________
DMA channels of other boards ___________________________________________________
Interrupt level of other boards ___________________________________________________
Documentation Comment Form
National Instruments encourages you to comment on the documentation supplied with our
products. This information helps us provide quality products to meet your needs.
Title:
SCXI-1200 User Manual
Edition Date:
December 1996
Part Number:
320673C-01
Please comment on the completeness, clarity, and organization of the manual.
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If you find errors in the manual, please record the page numbers and describe the errors.
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Glossary
Prefix
Meaning
Value
p-
pico-
10-12
n-
nano-
10-9
µ-
micro-
10-6
m-
milli-
10-3
k-
kilo-
103
M-
mega-
106
G-
giga-
109
Symbols
>
greater than
≥
greater than or equal to
<
less than
%
percent
+
positive of, or plus
-
negative of, or minus
/
per
°
degree
±
plus or minus
Ω
ohms
© National Instruments Corporation
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SCXI-1200 User Manual
Glossary
A
A
amperes
AC
alternating current
ACH<0..7>
Analog Channel signal
ACK*
Acknowledge Input signal
A/D
analog-to-digital
ADC
analog-to-digital converter–an electronic device, often an
integrated circuit, that converts an analog voltage to a digital
number
ADC resolution
the resolution of the ADC, which is measured in bits. An ADC
with 16 bits has a higher resolution, and thus a higher degree of
accuracy, than a 12-bit ADC.
AGND
Analog Ground signal
AISENSE/AIGND
Analog Input Sense/Analog Input Ground signal
alias
a false lower frequency component that appears in sampled data
acquired at too low a sampling rate
amplification
a type of signal conditioning that improves accuracy in the
resulting digitized signal and reduces noise
amplitude flatness
a measure of how close to constant the gain of a circuit remains
over a range of frequencies
ANSI
American National Standards Institute
asynchronous
(1) hardware–a property of an event that occurs at an arbitrary
time, without synchronization to a reference clock (2) software–a
property of a function that begins an operation and returns prior
to the completion or termination of the operation
AWG
American Wire Gauge
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© National Instruments Corporation
Glossary
B
b
bit–one binary digit, either 0 or 1
B
byte–eight related bits of data, an eight-bit binary number; also
used to denote the amount of memory required to store one byte
of data
base address
a memory address that serves as the starting address for
programmable registers; all other addresses are located by adding
to the base address.
baud rate
serial communications data transmission rate expressed in bits per
second (b/s)
binary
a number system with a base of 2
BIOS
basic input/output system–BIOS functions are the fundamental
level of any PC or compatible computer. BIOS functions embody
the basic operations needed for successful use of the computer’s
hardware resources.
bipolar
a signal range that includes both positive and negative values (for
example, -5 V to +5 V)
buffer
temporary storage for acquired or generated data
bus
the group of conductors that interconnect individual circuitry in a
computer. Typically, a bus is the expansion vehicle to which I/O
or other devices are connected. Examples of PC buses are the AT
bus, NuBus, Micro Channel, and EISA bus.
C
C
Celsius
CalDAC
Calibration DAC
cascading
process of extending the counting range of a counter chip by
connecting to the next higher counter
CCLKB1
Counter B1 Clock signal
© National Instruments Corporation
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SCXI-1200 User Manual
Glossary
channel
pin or wire lead to which you apply or from which you read the
analog or digital signal. Analog signals can be single-ended or
differential. For digital signals, you group channels to form ports.
Ports usually consist of either four or eight digital channels.
circuit trigger
a condition for starting or stopping clocks
CLKB2
Counter B2 Clock signal
clock
hardware component that controls timing for reading from or
writing to groups
cm
centimeters
CMOS
complementary metal-oxide semiconductor
CMRR
common-mode rejection ratio–A measure of an instrument’s
ability to reject interference from a common-mode signal, usually
expressed in decibels (dB).
code width
the smallest detectable change in an input voltage of a DAQ
device
common-mode range
the input range over which a circuit can handle a common-mode
signal
common-mode signal
the mathematical average voltage, relative to the computer’s
ground, of the signals from a differential input
common-mode voltage
any voltage present at the instrumentation amplifier inputs with
respect to amplifier ground
conditional retrieval
a method of triggering in which you simulate an analog trigger
using software. Also called software triggering.
conversion device
device that transforms a signal from one form to another. For
example, analog-to-digital converters (ADCs) for analog input,
digital-to-analog converters (DACs) for analog output, digital
input or output ports, and counter/timers are conversion devices.
conversion time
the time required, in an analog input or output system, from the
moment a channel is interrogated (such as with a read instruction)
to the moment that accurate data is available
counter/timer
a circuit that counts external pulses or clock pulses (timing)
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© National Instruments Corporation
Glossary
coupling
the manner in which a signal is connected from one location to
another
COUTB1
Counter B1 Output signal
crosstalk
an unwanted signal on one channel due to an input on a different
channel
current drive capability
the amount of current a digital or analog output channel is capable
of sourcing or sinking while still operating within voltage range
specifications
current sinking
the ability of a DAQ board to dissipate current for analog or
digital output signals
current sourcing
the ability of a DAQ board to supply current for analog or digital
output signals
D
D/A
digital-to-analog
D*/A
Data/Address signal
DAC
digital-to-analog converter–an electronic device, often an
integrated circuit, that converts a digital number into a
corresponding analog voltage or current
DAC0OUT
Digital-to-Analog Converter 0 and 1 Output signal
DAQ
data acquisition–(1) collecting and measuring electrical signals
from sensors, transducers, and test probes or fixtures and
inputting them to a computer for processing; (2) collecting and
measuring the same kinds of electrical signals with A/D and/or
DIO boards plugged into a computer, and possibly generating
control signals with D/A and/or DIO boards in the same computer
DAQD*/A
Data acquisition board data/address line signal
DATA
Data Lines at the Specified Port signal
dB
decibel–the unit for expressing a logarithmic measure of the ratio
of two signal levels: dB=20log10 V1/V2, for signals in volts
© National Instruments Corporation
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SCXI-1200 User Manual
Glossary
DC
direct current
default setting
a default parameter value recorded in the driver. In many cases,
the default input of a control is a certain value (often 0) that means
use the current default setting. For example, the default input for
a parameter may be do not change current setting. If you do
change the value of such a parameter, the new value becomes the
new setting. You can set default settings for some parameters in
the configuration utility or manually using switches located on the
device.
device
a plug-in data acquisition board, card, or pad that can contain
multiple channels and conversion devices. Plug-in boards,
PCMCIA cards, and devices such as the DAQPad-1200, which
connects to your computer parallel port, are all examples of DAQ
devices. SCXI modules are distinct from devices, with the
exception of the SCXI-1200, which is a both a module and a
device.
DIFF
differential mode
differential input
an analog input consisting of two terminals, both of which are
isolated from computer ground, whose difference is measured
differential measurement
system
a way you can configure your device to read signals, in which you
do not need to connect either input to a fixed reference, such as
the earth or a building ground
digital port
See port.
DIN
Deutsche Industrie Norme
DIO
digital input/output
DGND
digital ground signal
DNL
differential nonlinearity–a measure in LSB of the worst-case
deviation of code widths from their ideal value of 1 LSB
DOS
disk operating system
drivers
software that controls a specific hardware device such as a DAQ
board or a GPIB interface board
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© National Instruments Corporation
Glossary
dynamic range
the ratio of the largest signal level a circuit can handle to the
smallest signal level it can handle (usually taken to be the noise
level), normally expressed in dB
E
EEPROM
electrically erased programmable read-only memory–ROM that
can be erased with an electrical signal and reprogrammed
EMC
electromechanical compliance
external trigger
a voltage pulse from an external source that triggers an event such
as A/D conversion
EXTCONV*
External Convert signal
EXTTRIG
External Trigger signal
EXTUPDATE*
External Update signal
F
FIFO
first-in first-out memory buffer–the first data stored is the first
data sent to the acceptor. FIFOs are often used on DAQ devices to
temporarily store incoming or outgoing data until that data can be
retrieved or output. For example, an analog input FIFO stores the
results of A/D conversions until the data can be retrieved into
system memory, a process that requires the servicing of interrupts
and often the programming of the DMA controller. This process
can take several milliseconds in some cases. During this time,
data accumulates in the FIFO for future retrieval. With a larger
FIFO, longer latencies can be tolerated. In the case of analog
output, a FIFO permits faster update rates, because the waveform
data can be stored on the FIFO ahead of time. This again reduces
the effect of latencies associated with getting the data from system
memory to the DAQ device.
filtering
a type of signal conditioning that allows you to filter unwanted
signals from the signal you are trying to measure
© National Instruments Corporation
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Glossary
floating signal sources
signal sources with voltage signals that are not connected to an
absolute reference or system ground. Also called nonreferenced
signal sources. Some common example of floating signal sources
are batteries, transformers, or thermocouples.
ft
feet
G
Gabor Spectrogram
a new algorithm for joint time-frequency analysis that uses the
discrete Gabor transform. The Gabor Spectrogram produces a
three-dimensional plot of signal power versus frequency and time.
Used in sonar, acoustics, and vibration analysis.
gain
the factor by which a signal is amplified, sometimes expressed in
decibels
gain accuracy
a measure of deviation of the gain of an amplifier from the ideal
gain
GATB<0..2>
Counter B0, B1, and B2 gate signals
GATE input pin
a counter input pin that controls when counting occurs in your
application
grounded measurement system See referenced single-ended mode.
H
handshaked digital I/O
a type of digital acquisition/generation where a device or module
accepts or transfers data after a digital pulse has been received.
Also called latched digital I/O.
hardware
the physical components of a computer system, such as the circuit
boards, plug-in boards, chassis, enclosures, peripherals, cables,
and so on
hardware triggering
a form of triggering where you set the start time of an acquisition
and gather data at a known position in time relative to a trigger
signal.
hex
hexadecimal
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© National Instruments Corporation
Glossary
Hz
hertz–the number of scans read or updates written per second
I
IBF
Input Buffer Full signal
in.
inches
INL
integral nonlinearity–a measure in LSB of the worst-case
deviation from the ideal A/D or D/A transfer characteristic of the
analog I/O circuitry
input bias current
the current that flows into the inputs of a circuit
input impedance
the measured resistance and capacitance between the input
terminals of a circuit
input offset current
the difference in the input bias currents of the two inputs of an
instrumentation amplifier
instrumentation amplifier
a circuit whose output voltage with respect to ground is
proportional to the difference between the voltages at its two
inputs
interrupt
a computer signal indicating that the CPU should suspend its
current task to service a designated activity
interrupt level
the relative priority at which a device can interrupt
interval scanning
scanning method where there is a longer interval between scans
than there is between individual channels comprising a scan
INTR
Interrupt Request signal
I/O
input/output–the transfer of data to/from a computer system
involving communications channels, operator interface devices,
and/or data acquisition and control interfaces
IOH
current, output high
IOL
current, output low
IRQ
interrupt request
ISA
industry standard architecture
© National Instruments Corporation
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SCXI-1200 User Manual
Glossary
K
k
kilo–the standard metric prefix for 1,000, or 103, used with units
of measure such as volts, hertz, and meters
K
kilo–the prefix for 1,024, or 210, used with B in quantifying data
or computer memory
kbytes/s
a unit for data transfer that means 1,000 or 103 bytes/s
kS
1,000 samples
L
latched digital I/O
a type of digital acquisition/generation where a device or module
accepts or transfers data after a digital pulse has been received.
Also called handshaked digital I/O.
library
a file containing compiled object modules, each comprised of one
of more functions, that can be linked to other object modules that
make use of these functions. NIDAQMSC.LIB is a library that
contains NI-DAQ functions. The NI-DAQ function set is broken
down into object modules so that only the object modules that are
relevant to your application are linked in, while those object
modules that are not relevant are not linked.
linearity
the adherence of device response to the equation R = KS, where
R = response, S = stimulus, and K = a constant
LSB
least significant bit
M
m
meters
M
(1) mega, the standard metric prefix for 1 million or 106, when
used with units of measure such as volts and hertz; (2) mega, the
prefix for 1,048,576, or 220, when used with B to quantify data or
computer memory.
max
maximum
MB
megabytes of memory
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© National Instruments Corporation
Glossary
memory buffer
See buffer.
min
minimum
MIO
multifunction I/O
MSB
most significant bit
MTBF
mean time between failure
multiplexed mode
an SCXI operating mode in which analog input channels are
multiplexed into one module output so that your cabled DAQ
device has access to the module’s multiplexed output as well as
the outputs on all other multiplexed modules in the chassis
through the SCXI bus. Also called serial mode.
mux
multiplexer–a switching device with multiple inputs that
sequentially connects each of its inputs to its output, typically at
high speeds, in order to measure several signals with a single
analog input channel
N
NI-DAQ
NI driver software for DAQ hardware
noise
an undesirable electrical signal. Noise comes from external
sources such as the AC power line, motors, generators,
transformers, fluorescent lights, soldering irons, CRT displays,
computers, electrical storms, welders, radio transmitters, and
internal sources such as semiconductors, resistors, and capacitors.
Noise corrupts signals you are trying to send or receive.
nonlatched digital I/O
a type of digital acquisition/generation where LabVIEW updates
the digital lines or port states immediately or returns the digital
value of an input line. Also called immediate digital I/O or nonhandshaking.
nonreferenced signal sources
signal sources with voltage signals that are not connected to an
absolute reference or system ground. Also called floating signal
sources. Some common example of nonreferenced signal sources
are batteries, transformers, or thermocouples.
© National Instruments Corporation
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Glossary
NRSE
nonreferenced single-ended mode–all measurements are made
with respect to a common (NRSE) measurement system
reference, but the voltage at this reference can vary with respect
to the measurement system ground
Nyquist Sampling Theorem
a law of sampling theory stating that if a continuous bandwidthlimited signal contains no frequency components higher than half
the frequency at which it is sampled, then the original signal can
be recovered without distortion
O
OBF*
Output Buffer Full signal
onboard channels
channels provided by the plug-in data acquisition board
operating system
base-level software that controls a computer, runs programs,
interacts with users, and communicates with installed hardware or
peripheral devices
OUTB0, OUTB1
counter B0, B1 output signals
output settling time
the amount of time required for the analog output voltage to reach
its final value within specified limits
output slew rate
the maximum rate of change of analog output voltage from one
level to another
P
PA, PB, PC<0..7>
Port A, B, or C 0 through 7 signal
parallel mode
a type of SCXI operating mode in which the module sends each of
its input channels directly to a separate analog input channel of
the device to the module
PGIA
programmable gain instrumentation amplifier
port
(1) a communications connection on a computer or a remote
controller (2) a digital port, consisting of four or eight lines of
digital input and/or output
postriggering
the technique used on a DAQ board to acquire a programmed
number of samples after trigger conditions are met
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© National Instruments Corporation
Glossary
ppm
parts per million
pretriggering
the technique used on a DAQ board to keep a continuous buffer
filled with data, so that when the trigger conditions are met, the
sample includes the data leading up to the trigger condition
propagation
the transmission of a signal through a computer system
propagation delay
the amount of time required for a signal to pass through a circuit
protocol
the exact sequence of bits, characters, and control codes used to
transfer data between computers and peripherals through a
communications channel
Q
quantization error
the inherent uncertainty in digitizing an analog value due to the
finite resolution of the conversion process
R
RD*
Read signal
referenced signal sources
Signal sources with voltage signals that are referenced to a system
ground, such as the earth or a building ground. Also called
grounded signal sources.
relative accuracy
a measure in LSB of the accuracy of an ADC. It includes all nonlinearity and quantization errors. It does not include offset and
gain errors of the circuitry feeding the ADC.
resolution
the smallest signal increment that can be detected by a
measurement system. Resolution can be expressed in bits, in
proportions, or in percent of full scale. For example, a system has
12-bit resolution, one part in 4,096 resolution, and 0.0244 percent
of full scale.
rms
root mean square
RSE
referenced single-ended mode–all measurements are made with
respect to a common reference measurement system or a ground.
Also called a grounded measurement system.
© National Instruments Corporation
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Glossary
S
s
seconds
S
samples
sample counter
the clock that counts the output of the channel clock, in other
words, the number of samples taken. On boards with simultaneous
sampling, this counter counts the output of the scan clock and
hence the number of scans.
scan
one or more analog or digital input samples. Typically, the
number of input samples in a scan is equal to the number of
channels in the input group. For example, one pulse from the scan
clock produces one scan which acquires one new sample from
every analog input channel in the group.
SCXI
Signal Conditioning eXtensions for Instrumentation–the National
Instruments product line for conditioning low-level signals within
an external chassis near sensors so only high-level signals are sent
to DAQ boards in the noisy PC environment
SDK
software development kit
SE
single-ended–a term used to describe an analog input that is
measured with respect to a common ground
sensor
a device that responds to a physical stimulus (heat, light, sound,
pressure, motion, flow, and so on), and produces a corresponding
electrical signal
SERCLK
Serial Clock signal
SERDATIN
Serial Data In signal
SERDATOUT
Serial Data Out signal
settling time
the amount of time required for a voltage to reach its final value
within specified limits
signal conditioning
the manipulation of signals to prepare them for digitizing
SLOT0SEL*
Slot 0 Select signal
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© National Instruments Corporation
Glossary
SNR
signal-to-noise ratio–the ratio of the overall rms signal level to the
rms noise level, expressed in dB
software trigger
a programmed event that triggers an event such as data acquisition
software triggering
a method of triggering in which you to simulate an analog trigger
using software. Also called conditional retrieval.
SOURCE input pin
a counter input pin where the counter counts the signal transitions
SPICLK
Serial Peripheral Interface Clock signal
SS*
Slot-Select signal
S/s
samples per second–used to express the rate at which a DAQ
board samples an analog signal
strain gauge
a thin conductor, which is attached to a material, that detects
stress or vibrations in that material. The conductor’s resistance is
a function of the applied force.
STB*
Strobe Input signal
synchronous
(1) hardware–a property of an event that is synchronized to a
reference clock (2) software–a property of a function that begins
an operation and returns only when the operation is complete
system noise
a measure of the amount of noise seen by an analog circuit or an
ADC when the analog inputs are grounded
T
THD
total harmonic distortion–the ratio of the total rms signal due to
harmonic distortion to the overall rms signal, in dB or percent
THD+N
signal-to-THD plus noise–the ratio in decibels of the overall rms
signal to the rms signal of harmonic distortion plus noise
introduced
thermistor
a semiconductor sensor that exhibits a repeatable change in
electrical resistance as a function of temperature. Most
thermistors exhibit a negative temperature coefficient.
© National Instruments Corporation
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Glossary
thermocouple
a temperature sensor created by joining two dissimilar metals.
The junction produces a small voltage as a function of the
temperature.
transducer
See sensor.
transducer excitation
a type of signal conditioning that uses external voltages and
currents to excite the circuitry of a signal conditioning system into
measuring physical phenomena
transfer rate
the rate, measured in bytes/s, at which data is moved from source
to destination after software initialization and set up operations;
the maximum rate at which the hardware can operate
trigger
any event that causes or starts some form of data capture
TTL
transistor-transistor logic
U
unipolar
a signal range that is always positive (for example, 0 to +10 V)
UP/BP*
Unipolar/bipolar bit
update
the output equivalent of a scan. One or more analog or digital
output samples. Typically, the number of output samples in an
update is equal to the number of channels in the output group. For
example, one pulse from the update clock produces one update
which sends one new sample to every analog output channel in the
group.
update rate
the number of output updates per second
V
V
volts
VDC
volts direct current
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© National Instruments Corporation
Glossary
VI
Virtual Instrument–(1) a combination of hardware and/or
software elements, typically used with a PC, that has the
functionality of a classic stand-alone instrument. (2) a LabVIEW
software module (VI) that consists of a front panel user interface
and a block diagram program
VIH
volts, input high
VIL
volts, input low
Vin
volts in
VOH
volts, output high
VOL
volts, output low
W
W
watts
waveform
multiple voltage readings taken at a specific sampling rate
wire
data path between nodes.
WR*
Write signal
© National Instruments Corporation
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Index
Numbers
analog input configuration, 2-6 to 2-9. See also
analog input signal connections.
bit configurations (table), 2-5
DIFF input
definition (table), 2-7
description, 2-8
factory configuration, 2-5
NRSE input
definition (table), 2-7
description, 2-8
polarity and range, 2-9
RSE input
definition (table), 2-7
description, 2-8
analog input multiplexers, 4-3
analog input signal connections, 3-4 to 3-6
common-mode signal rejection
considerations, 3-13
DIFF configuration, 3-7 to 3-8
definition, 3-7
floating signal sources, 3-9 to 3-10
grounded signal sources, 3-8 to 3-9
when to use, 3-7
single-ended signal connections
definition, 3-10
floating signal sources (RSE configuration),
3-11
grounded signal sources (NRSE
configuration), 3-11 to 3-12
when to use, 3-10
analog input specifications, A-1 to A-6
amplifier characteristics, A-3
dynamic characteristics, A-4
explanation, A-4 to A-6
DAQ rates, A-6
differential nonlinearity, A-5
+5 V signal, 3-4
A
ACH<0..7> signal
description (table), 3-3
input ranges and maximum ratings, 3-4
ACK* signal
description (table), 3-18
mode 1 output timing (figure), 3-20
mode 2 bidirectional timing (figure), 3-21
A/D FIFO, 4-4
ADC (analog to digital converter), 4-4
AGND signal, 3-3
AISENSE/AIGND signal
analog input signal connections, 3-4
description (table), 3-3
NRSE configuration (table), 2-7
amplifier characteristics, A-3
analog input and DAQ circuitry, 4-2 to 4-8
bipolar analog input signal range versus
gain (table), 4-7 to 4-8
block diagram, 4-3
DAQ rates, 4-6 to 4-8
DAQ timing circuitry, 4-4 to 4-8
description, 4-3 to 4-4
maximum recommended data acquisition
rates (table), 4-7
multiple-channel (scanned) data acquisition,
4-5 to 4-6
overview, 4-2 to 4-3
settling time versus gain (table), 4-7
single-channel data acquisition, 4-5
unipolar analog input signal range versus
gain (table), 4-8
© National Instruments Corporation
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Index
bulletin board support, C-1
dither, A-6
integral nonlinearity, A-5
relative accuracy, A-4 to A-5
system noise, A-5 to A-6
input characteristics, A-1 to A-2
transfer characteristics, A-2 to A-3
analog output circuitry, 4-8 to 4-10
analog output configuration
bit configurations (table), 2-5
description, 2-6
factory configuration, 2-5
unipolar or bipolar output, 2-6
analog output signal connections
digital I/O signal connections, 3-14 to
3-16
making connections (figure), 3-14
pins for, 3-13
Port C pin connections, 3-17
timing specifications
Mode 1 input timing (figure), 3-19
Mode 1 timing for output transfers
(figure), 3-20
Mode 2 bidirectional timing (figure),
3-21
signals for (table), 3-18
analog output specifications, A-7 to A-8
differential nonlinearity, A-8
dynamic characteristics, A-8
explanation, A-8
output characteristics, A-7
relative accuracy, A-8
transfer characteristics, A-7
voltage output, A-7 to A-8
analog to digital converter (ADC), 4-4
C
cables
custom, 1-5 to 1-6
parallel port, troubleshooting, B-2 to B-3
Calibrate-1200 function, 5-3
calibration
calibration DACs, 5-1
EEPROM storage, 5-1 to 5-2
equipment requirements, 5-3
factory calibration, 5-2
higher gains, 5-2
overview, 5-1 to 5-2
using Calibrate-1200 function, 5-3
CLK signal, in general-purpose timing signal
connections, 3-26 to 3-29
CLKB1 signal, 3-4
CLKB2 signal, 3-4
common-mode signal rejection, 3-13
configuration, 2-2 to 2-10. See also
installation.
analog input, 2-6 to 2-9
bit configurations (table), 2-5
DIFF input, 2-7 (table), 2-8
factory configuration, 2-5
NRSE input, 2-7 (table), 2-8
polarity and range, 2-9
RSE input, 2-7 (table), 2-8
analog output
bit configurations (table), 2-5
description, 2-6
factory configuration, 2-5
hazardous voltage warnings, 2-4 to 2-5
parts locator diagram (figure), 2-4
SCXI circuitry, 2-9 to 2-10
SCXI configurations, 4-17 to 4-18
CONVERT signal
posttrigger DAQ timing (figure)
case 1, 3-23
case 2, 3-24
pretrigger DAQ timing (figure), 3-25
B
bipolar analog input
configuration settings (table), 2-5
polarity and range configuration, 2-9
signal range versus gain (table), 4-7 to 4-8
bipolar analog output configuration, 2-6
settings (table), 2-5
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© National Instruments Corporation
Index
pretrigger data acquisition timing
(figure), 3-25
DAQD*/A signal, 3-30
DATA signal
description (table), 3-18
mode 1 input timing (figure), 3-19
mode 1 output timing (figure), 3-20
mode 2 bidirectional timing (figure), 3-21
DGND signal (table), 3-3, 3-4
differential (DIFF) input configuration
definition (table), 2-7
description, 2-8
differential nonlinearity
analog input specifications, A-5
analog output specifications, A-8
differential signal connections (DIFF
configuration), 3-7 to 3-8
definition, 3-7
floating signal sources, 3-9 to 3-10
grounded signal sources, 3-8 to 3-9
when to use, 3-7
digital I/O circuitry, 4-10
digital I/O signal connections, 3-14 to 3-16
pins for, 3-14
SCXIbus, 3-30 to 3-31
specifications and ratings, 3-15
typical applications (figure), 3-16
digital I/O specifications, A-8 to A-9
digital to analog converter (DAC), 4-9
direct parallel port connection to PC, 2-3
dither circuitry, A-6
documentation
conventions used in manual, x-xi
National Instruments documentation set,
xi-xii
organization of manual, ix-x
related documentation, xii
dynamic characteristics
analog input specifications, A-4
analog output specifications, A-8
counter block diagram, 4-12
counter/timer signals. See general-purpose
timing signal connections and counter/timer
signals.
COUTB1 signal, 2-9
custom cables, 1-5 to 1-6
customer communication, xii, C-1 to C-2
D
DAC (digital to analog converter), 4-9
DAC0OUT signal
analog output circuitry, 4-9
analog output signal connections, 3-13 to
3-14
description (table), 3-3
DAC1OUT signal
analog output circuitry, 4-9
analog output signal connections, 3-13 to
3-14
description (table), 3-3
DAQ circuitry, 4-4 to 4-8
bipolar analog input signal range versus
gain (table), 4-7 to 4-8
block diagram, 4-3
DAQ rates, 4-6 to 4-8, A-6
maximum recommended data acquisition
rates (table), 4-7
multiple-channel (scanned) data
acquisition, 4-5 to 4-6
overview, 4-2 to 4-3
settling time versus gain (table), 4-7
single-channel data acquisition, 4-5
timing circuitry, 4-4 to 4-8
unipolar analog input signal range versus
gain (table), 4-8
DAQ timing connections, 3-22 to 3-26
EXTCONV* signal timing (figure), 3-22
EXTUPDATE* signal timing for
updating DAC output (figure), 3-26
posttrigger data acquisition timing
case 1 (figure), 3-23
case 2 (figure), 3-24
© National Instruments Corporation
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Index
E
(figure), 3-7
requirements, 3-6
single-ended connections, 3-10
frequency measurement, 3-28
application (figure), 3-28
front connector. See signal connections.
FTP support, C-1
fuse, 2-4, A-10
e-mail support, C-2
EEPROM storage of calibration data, 5-1 to
5-2
electronic support services, C-1 to C-2
environment specifications, A-11
event counting, 3-26 to 3-27
application with external switch gating
(figure), 3-27
EXTCONV* signal
absolute maximum voltage input rating,
3-26
DAQ timing connections, 3-22 to 3-23
description (table), 3-3
posttrigger DAQ timing (figure)
case 1, 3-23
case 2, 3-24
pretrigger DAQ timing (figure), 3-25
SCXI configuration, 2-9
timing requirements (figure), 3-22
EXTTRIG signal
DAQ timing connections, 3-22 to 3-25
description (table), 3-3
posttrigger DAQ timing (figure)
case 1, 3-23
case 2, 3-24
pretrigger DAQ timing (figure), 3-25
EXTUPDATE* signal
absolute maximum voltage input rating,
3-26
analog output circuitry, 4-9
DAQ timing connections, 3-25 to 3-26
description (table), 3-3
timing for updating DAC output (figure),
3-26
G
GATB0 signal, 3-3
GATB1 signal, 3-4
GATB2 signal, 3-4
GATE signal, in general-purpose timing
signal connections, 3-26 to 3-30
general-purpose timing signal connections and
counter/timer signals, 3-26 to 3-30
event counting, 3-26 to 3-27
application with external switch
gating (figure), 3-27
frequency measurement, 3-28
application (figure), 3-28
general-purpose timing signals (figure),
3-29
pulse-width measurement, 3-27
specifications and ratings for 82C53 I/O
signals, 3-28 to 3-29
time-lapse measurement, 3-27
ground-referenced signal sources
description, 3-6
differential connections, 3-8 to 3-9
recommended input configurations
(figure), 3-7
single-ended connections, 3-11 to 3-12
F
fax and telephone support, C-2
FaxBack support, C-2
floating signal sources
differential connections, 3-9 to 3-10
recommended input configurations
SCXI-1200 User Manual
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© National Instruments Corporation
Index
H
J
hardware installation. See installation.
hazardous voltage warnings, 2-4 to 2-5
HOLDTRIG signal, 3-30
HWTRIG mode, 3-22 to 3-23
jumper settings for SCXI-1200, 2-9 to 2-10
L
LabVIEW and LabWindows/CVI application
software, 1-3
I
IBF signal
description (table), 3-18
mode 1 input timing (figure), 3-19
mode 2 bidirectional timing (figure), 3-21
input characteristics, analog input
specifications, A-1 to A-2
input modes. See analog input configuration.
installation. See also configuration.
hardware installation, 2-1 to 2-2
troubleshooting, B-1 to B-3
IRQ level, B-2
parallel port address, B-1 to B-2
parallel port cable, B-2 to B-3
PCMCIA cards, B-2
unpacking the SCXI-1200, 1-6
instrumentation amplifier, 2-7, 3-5
integral nonlinearity, analog input
specifications, A-5
interrupts for parallel ports, 2-3, B-2
interval-scanning timing
single-channel interval timing (figure),
4-14
two-channel interval-scanning timing
(figure), 4-13
INTR signal
description (table), 3-18
mode 1 input timing (figure), 3-19
mode 1 output timing (figure), 3-20
mode 2 bidirectional timing (figure), 3-21
M
manual. See documentation.
mode 1 input timing (figure), 3-19
mode 1 timing for output transfers (figure),
3-20
mode 2 bidirectional timing (figure), 3-21
module configuration. See configuration.
multiple-channel (scanned) data acquisition,
4-5 to 4-6
N
NI-DAQ driver software, 1-3 to 1-4
noise, system, A-5 to A-6
nonlinearity
differential
analog input specifications, A-5
analog output specifications, A-8
integral, A-5
NRSE (nonreferenced single-ended) input
configuration
definition (table), 2-7
description, 2-8
single-ended connections for grounded
signal sources, 3-11 to 3-12
O
OBF* signal
description (table), 3-18
mode 1 output timing (figure), 3-20
mode 2 bidirectional timing (figure), 3-21
© National Instruments Corporation
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SCXI-1200 User Manual
Index
operation of SCXI-1200. See theory of
operation.
OUT signal, in general-purpose signal
connections, 3-26 to 3-30
OUTB0 signal, 3-3
OUTB1 signal, 3-4
OUTB2 signal, 3-4
output characteristics, analog output
specifications, A-7
mode 2 bidirectional timing (figure), 3-21
register-level programming, 1-4 to 1-5
relative accuracy
analog input specifications, A-4 to A-5
analog output specifications, A-8
RSE (referenced single-ended) input
configuration
definition (table), 2-7
description, 2-8
single-ended connections for floating
signal sources, 3-10
P
PA<0..7> signal, 3-3
parallel ports
IBM-compatible PCs, 2-3
installation troubleshooting, B-1 to B-3
address for parallel port, B-1 to B-2
cable problems, B-2 to B-3
IRQ level, B-2
PCMCIA cards, B-2
specifications, A-10
PB<0..7> signal, 3-3
PC<0..7> signal, 3-3
physical specifications, A-11
pin assignments for front connector (figure),
3-2
Port C pin connections, 3-17
signal assignments (table), 3-17
posttrigger data acquisition timing
case 1 (figure), 3-23
case 2 (figure), 3-24
power requirement specifications, A-10
PRETRIG mode, 3-22, 3-24
pretrigger data acquisition timing (figure),
3-25
programmable gain amplifier, 4-4
pulse-width measurement, 3-27
S
SCANCLK signal
digital I/O signal connections, 3-30
multiple-module multiplexed scanning,
4-15 to 4-16
SCANCON signal, multiple-module
multiplexed scanning, 4-15 to 4-16
scanned (multiple-channel) data acquisition,
4-5 to 4-6
scanning modes, SCXI
multiple-module multiplexed scanning,
4-15 to 4-18
single-module parallel scanning, 4-15
SCXI digital interface, 4-14 to 4-18
block diagram, 4-14
multiple-module multiplexed scanning,
4-15 to 4-18
SCXI configurations with SCXI-1200,
4-17 to 4-18
single-module parallel scanning, 4-15
SCXI-1200
block diagram, 4-1
optional equipment, 1-5 to 1-6
overview and features, 1-1 to 1-2
requirements for getting started, 1-2
software programming choices
LabVIEW and LabWindows/CVI
application software, 1-3
NI-DAQ driver software, 1-3 to 1-4
R
RD* signal
description (table), 3-18
mode 1 input timing (figure), 3-19
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© National Instruments Corporation
Index
timing connections
data acquisition, 3-22 to 3-26
digital I/O signal connections for
SCXIbus, 3-30 to 3-31
event counting, 3-26 to 3-27
application with external switch
gating (figure), 3-27
EXTUPDATE* signal timing for
updating DAC output (figure), 3-26
frequency measurement, 3-28
frequency measurement application
(figure), 3-28
general-purpose timing connections
and counter/timer signals, 3-26 to
3-30
general-purpose timing signal
requirements (figure), 3-29
pins for, 3-22
posttrigger data acquisition timing
case 1 (figure), 3-23
case 2 (figure), 3-24
pretrigger data acquisition timing
(figure), 3-25
pulse-width measurement, 3-27
specifications and ratings for 82C53
I/O signals, 3-28 to 3-29
time-lapse measurement, 3-27
timing specifications
mode 1 input timing (figure), 3-19
mode 1 timing for output transfers
(figure), 3-20
mode 2 bidirectional timing (figure),
3-21
signals for (table), 3-18
warning against exceeding maximum
ratings, 3-1
single-channel data acquisition, 4-5
single-ended signal connections
definition, 3-10
floating signal sources (RSE
configuration), 3-11
grounded signal sources (NRSE
configuration), 3-11 to 3-12
register-level programming, 1-4 to
1-5
unpacking, 1-6
SCXIbus digital I/O signal connections, 3-30
to 3-31
SERCLK signal, 3-30
SERDATOUT signal, 3-30
signal connections
analog input, 3-4 to 3-6
analog output, 3-13 to 3-21
common-mode signal rejection, 3-13
differential connections
definition, 3-7
floating signal sources, 3-9 to 3-10
grounded signal sources, 3-8 to 3-9
when to use, 3-6
digital I/O signal connections, 3-14 to
3-16
floating signal sources, 3-6
differential connections, 3-9 to 3-10
recommended input configurations
(figure), 3-7
single-ended connections, 3-10
front connector pin assignments (figure),
3-2
ground-referenced signal sources, 3-6
differential connections, 3-8 to 3-9
recommended input configurations
(figure), 3-7
single-ended connections, 3-11 to
3-12
input configurations, 3-7 to 3-13
Port C pin connections, 3-17
SCXI-1200 instrumentation amplifier,
3-5
signal descriptions, 3-2 to 3-4
single-ended connections
definition, 3-10
floating signal sources (RSE
configuration), 3-11
grounded signal sources (NRSE
configuration), 3-11 to 3-12
when to use, 3-10
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SCXI-1200 User Manual
Index
DAQ rates, 4-6 to 4-8
description, 4-3 to 4-4
maximum recommended data
acquisition rates (table), 4-7
overview, 4-2 to 4-3
unipolar analog input signal range
versus gain (table), 4-8
analog input and data acquisition circuitry
block diagram, 4-3
DAQ timing circuitry, 4-4 to 4-8
multiple-channel (scanned) data
acquisition, 4-5 to 4-6
settling time versus gain (table), 4-7
single-channel data acquisition, 4-5
analog output circuitry, 4-8 to 4-10
digital I/O circuitry, 4-10
functional overview, 4-1 to 4-2
SCXI digital interface, 4-14 to 4-18
block diagram, 4-14
multiple-module multiplexed
scanning, 4-15 to 4-18
SCXI configurations with
SCXI-1200, 4-17 to 4-18
single-module parallel scanning,
4-15
SCXI-1200 block diagram, 4-1
timing I/O circuitry, 4-11 to 4-14
block diagram, 4-12
counter block diagram, 4-12
single-channel interval timing
(figure), 4-14
two-channel interval-scanning
timing (figure), 4-13
time-lapse measurement, 3-27
timing connections
DAQ timing connections, 3-22 to 3-26
EXTCONV* signal timing (figure),
3-22
EXTUPDATE* signal timing for
updating DAC output (figure), 3-26
posttrigger data acquisition timing
case 1 (figure), 3-23
case 2 (figure), 3-24
when to use, 3-10
SLOT0SEL* signal, 3-30
software programming choices
LabVIEW and LabWindows/CVI
application software, 1-3
NI-DAQ driver software, 1-3 to 1-4
register-level programming, 1-4 to 1-5
specifications
analog input, A-1 to A-6
amplifier characteristics, A-3
dynamic characteristics, A-4
explanation, A-4 to A-6
input characteristics, A-1 to A-2
transfer characteristics, A-2 to A-3
analog output, A-7 to A-8
dynamic characteristics, A-8
explanation, A-8
output characteristics, A-7
transfer characteristics, A-7
voltage output, A-7 to A-8
digital I/O, A-8 to A-9
environment, A-11
physical, A-11
power requirements, A-10
timing I/O, A-9 to A-10
specifications, timing. See timing
specifications.
specifications and ratings
82C53 I/O signals, 3-28 to 3-29
digital I/O signal connections, 3-15
STB* signal
description (table), 3-18
mode 1 input timing (figure), 3-19
mode 2 bidirectional timing (figure), 3-21
system noise, A-5 to A-6
T
technical support, C-1 to C-2
theory of operation
analog input and DAQ circuitry
bipolar analog input signal range
versus gain (table), 4-7 to 4-8
SCXI-1200 User Manual
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© National Instruments Corporation
Index
signal range versus gain (table), 4-8
unipolar analog output configuration, 2-6
unpacking the SCXI-1200, 1-6
pretrigger data acquisition timing
(figure), 3-25
digital I/O signal connections for
SCXIbus, 3-30 to 3-31
general-purpose signals and counter/timer
signals, 3-26 to 3-30
event counting, 3-26 to 3-27
event counting application with
external switch gating (figure),
3-27
frequency measurement, 3-28
frequency measurement application
(figure), 3-28
pulse-width measurement, 3-27
specifications and ratings for 8253 I/
O signals, 3-28 to 3-29
time-lapse measurement, 3-27
timing requirements (figure), 3-29
pins for, 3-22
timing I/O circuitry, 4-11 to 4-14
block diagram, 4-12
counter block diagram, 4-12
single-channel interval timing (figure),
4-14
specifications, A-9 to A-10
two-channel interval-scanning timing
(figure), 4-13
timing specifications
Mode 1 input timing (figure), 3-19
Mode 1 timing for output transfers
(figure), 3-20
Mode 2 bidirectional timing (figure), 3-21
signals for (table), 3-18
transfer characteristics
analog input specifications, A-2 to A-3
analog output specifications, A-7
TRIG0 signal, multiple-module multiplexed
scanning, 4-15 to 4-16
V
voltage output specifications, A-7 to A-8
W
WR* signal
description (table), 3-14
mode 1 output timing (figure), 3-20
mode 2 bidirectional timing (figure), 3-21
U
unipolar analog input
polarity and range configuration, 2-9
© National Instruments Corporation
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SCXI-1200 User Manual

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